diff --git a/app/controllers/check/supplementary.controller.js b/app/controllers/check/supplementary.controller.js
deleted file mode 100644
index 9799a05bb2..0000000000
--- a/app/controllers/check/supplementary.controller.js
+++ /dev/null
@@ -1,18 +0,0 @@
-'use strict'
-
-/**
- * Controller for /test/supplementary endpoints
- * @module SupplementaryController
- */
-
-const SupplementaryDataService = require('../../services/check/supplementary-data.service.js')
-
-async function index (request, h) {
-  const result = await SupplementaryDataService.go(request.query.region)
-
-  return h.response(result).code(200)
-}
-
-module.exports = {
-  index
-}
diff --git a/app/plugins/router.plugin.js b/app/plugins/router.plugin.js
index fe0929b4d3..6fdc1364e7 100644
--- a/app/plugins/router.plugin.js
+++ b/app/plugins/router.plugin.js
@@ -13,7 +13,6 @@
 
 const AssetRoutes = require('../routes/assets.routes.js')
 const BillRunRoutes = require('../routes/bill-runs.routes')
-const CheckRoutes = require('../routes/check.routes.js')
 const FilterRoutesService = require('../services/plugins/filter-routes.service.js')
 const HealthRoutes = require('../routes/health.routes.js')
 const RootRoutes = require('../routes/root.routes.js')
@@ -24,7 +23,6 @@ const routes = [
   ...RootRoutes,
   ...AssetRoutes,
   ...HealthRoutes,
-  ...CheckRoutes,
   ...BillRunRoutes
 ]
 
diff --git a/app/presenters/check/supplementary-data.presenter.js b/app/presenters/check/supplementary-data.presenter.js
deleted file mode 100644
index b85fbcba3f..0000000000
--- a/app/presenters/check/supplementary-data.presenter.js
+++ /dev/null
@@ -1,19 +0,0 @@
-'use strict'
-
-/**
- * Formats responses from the `SupplementaryDataService`
- * @module SupplementaryDataPresenter
- */
-
-function go (data) {
-  const chargeVersions = data.chargeVersions
-
-  return {
-    billingPeriods: data.billingPeriods,
-    chargeVersions
-  }
-}
-
-module.exports = {
-  go
-}
diff --git a/app/routes/check.routes.js b/app/routes/check.routes.js
deleted file mode 100644
index 8114d6205d..0000000000
--- a/app/routes/check.routes.js
+++ /dev/null
@@ -1,16 +0,0 @@
-'use strict'
-
-const SupplementaryController = require('../controllers/check/supplementary.controller.js')
-
-const routes = [
-  {
-    method: 'GET',
-    path: '/check/supplementary',
-    handler: SupplementaryController.index,
-    options: {
-      description: 'Used by the delivery team to check the SROC supplementary billing logic'
-    }
-  }
-]
-
-module.exports = routes
diff --git a/app/services/check/supplementary-data.service.js b/app/services/check/supplementary-data.service.js
deleted file mode 100644
index fa87895546..0000000000
--- a/app/services/check/supplementary-data.service.js
+++ /dev/null
@@ -1,32 +0,0 @@
-'use strict'
-
-/**
- * Confirms the billing periods, licences and charge versions used to generate an SROC supplementary bill run
- * @module SupplementaryDataService
- */
-
-const BillingPeriodService = require('../supplementary-billing/billing-period.service.js')
-const FetchChargeVersionsService = require('../supplementary-billing/fetch-charge-versions.service.js')
-const FetchRegionService = require('../supplementary-billing/fetch-region.service.js')
-const SupplementaryDataPresenter = require('../../presenters/check/supplementary-data.presenter.js')
-
-async function go (naldRegionId) {
-  const region = await FetchRegionService.go(naldRegionId)
-  const billingPeriods = BillingPeriodService.go()
-
-  // We know in the future we will be calculating multiple billing periods and so will have to iterate through each,
-  // generating bill runs and reviewing if there is anything to bill. For now, whilst our knowledge of the process
-  // is low we are focusing on just the current financial year, and intending to ship a working version for just it.
-  // This is why we are only passing through the first billing period; we know there is only one!
-  const chargeVersions = await FetchChargeVersionsService.go(region.regionId, billingPeriods[0])
-
-  return _response({ billingPeriods, chargeVersions })
-}
-
-function _response (data) {
-  return SupplementaryDataPresenter.go(data)
-}
-
-module.exports = {
-  go
-}
diff --git a/app/services/supplementary-billing/billing-period.service.js b/app/services/supplementary-billing/billing-period.service.js
index 4533a46fb0..df16a2c7fb 100644
--- a/app/services/supplementary-billing/billing-period.service.js
+++ b/app/services/supplementary-billing/billing-period.service.js
@@ -12,13 +12,13 @@
  * **IMPORTANT!** This service currently only handles SROC billing periods and only the 'current year'
  *
  * Using the current date at the time the service is called, it calculates the billing periods to use. We permit
- * changes to charge versions to be retroactively applied up to 5 years. So, a bill run generated in 2022 would need
- * to consider every financial year back to 2017.
+ * changes to charge versions to be retroactively applied up to 5 years. So, a bill run generated in 2022 would need to
+ * consider every financial year back to 2017.
  *
  * The exception to that is the change in charge scheme that happened in 2022, when we moved from ALCS (or PRESROC) to
  * SROC. Changes prior to 2022 would only apply to a ALCS bill run and vice versa.
  *
- * @returns {Object[]} an array of billing periods each containing a `startDate` and `endDate`.
+ * @returns {Object[]} An array of billing periods each containing a `startDate` and `endDate`.
  */
 function go () {
   // TODO: We have hardcoded the billing period this service returns to be 2022-23 the first year SROC went live. This
diff --git a/app/services/supplementary-billing/calculate-authorised-and-billable-days.service.js b/app/services/supplementary-billing/calculate-authorised-and-billable-days.service.js
index 815dd6e08c..daf83990ef 100644
--- a/app/services/supplementary-billing/calculate-authorised-and-billable-days.service.js
+++ b/app/services/supplementary-billing/calculate-authorised-and-billable-days.service.js
@@ -7,6 +7,8 @@
 
 const ConsolidateDateRangesService = require('./consolidate-date-ranges.service.js')
 
+const ONE_DAY_IN_MILLISECONDS = 24 * 60 * 60 * 1000
+
 /**
  * Returns the authorised and billable days for a given charge element based on its abstraction periods
  *
@@ -15,9 +17,9 @@ const ConsolidateDateRangesService = require('./consolidate-date-ranges.service.
  * start and end day and month, for example 1 Apr to 31 Oct. They do not have years because the intent is they are the
  * same period no matter what year it is.
  *
- * **Authorised** days is how much of the billing period overlaps with the abstraction period. **Billable** days is
- * how much of the charge period overlaps with the abstraction period (see params for explanations of billable and
- * charge periods).
+ * **Authorised** days is how much of the billing period overlaps with the abstraction period. **Billable** days is how
+ * much of the charge period overlaps with the abstraction period (see params for explanations of billable and charge
+ * periods).
  *
  * Calculating these values is complicated by the fact a charge element may have multiple abstraction periods. Added to
  * that abstraction periods do not intersect nicely with billing or charge periods. The abstraction period might start
@@ -28,34 +30,30 @@ const ConsolidateDateRangesService = require('./consolidate-date-ranges.service.
  * - **1 Jan 2023 to 30 Jun 2023** intersects as 1 Jan 2023 to 31 Mar 2023
  *
  * The number of days the abstraction period intersects either the billing or charge period is where we get our 'days'
- * from. The final complication is we cannot double count. If 2 charge purposes have abstraction periods that overlap
- * we must only count one of them. For example
+ * from. The final complication is we cannot double count. If 2 charge purposes have abstraction periods that overlap we
+ * must only count one of them. For example
  *
  * - charge purpose 1 has **1 Jan to 30 Jun**
  * - charge purpose 2 has **1 May to 31 Oct**
  *
- * They overlap 1 May to 30 Jun. To get our days we summate the result for each abstraction period and have to ensure
- * we only count this once.
+ * They overlap 1 May to 30 Jun. To get our days we summate the result for each abstraction period and have to ensure we
+ * only count this once.
  *
  * So, a charge purpose's abstraction dates might result in 2 relevant abstraction periods. A charge element might have
  * multiple charge purposes. But we must return a single **Authorised** and **Billable** days calculation. This problem
  * is what this service tackles.
  *
- * @param {Object} chargePeriod charge period is determined as the overlap between a charge version's start and end
- * dates, and the billing period's (financial year) start and end dates. So, when the charge version and billing period
- * are compared the charge period's start date is the latest of the two, and the end date is the earliest of their end
- * dates
- * @param {Date} chargePeriod.startDate
- * @param {Date} chargePeriod.endDate
- * @param {Object} billingPeriod the period a billing batch is being calculated for. Currently, this always equates to
- * a financial year, for example, 2022-04-01 to 2023-03-31
- * @param {Date} billingPeriod.startDate
- * @param {Date} billingPeriod.endDate
- * @param {module:ChargeElementModel} chargeElement referred to as the 'charge reference' in the UI, for example,
- * 4.1.10. A charge version can have multiple charge elements, though each will have a different reference. Each element
- * can have multiple charge purposes and it's these that hold the abstraction period data
- *
- * @returns {Object} an object containing an `authorisedDays` and `billableDays` property
+ * @param {{startDate: Date, endDate: Date}} chargePeriod Charge period is determined as the overlap between a charge
+ *  version's start and end dates, and the billing period's (financial year) start and end dates. So, when the charge
+ *  version and billing period are compared the charge period's start date is the latest of the two, and the end date is
+ *  the earliest of their end dates
+ * @param {{startDate: Date, endDate: Date}} billingPeriod The period a billing batch is being calculated for.
+ *  Currently, this always equates to a financial year, for example, 2022-04-01 to 2023-03-31
+ * @param {module:ChargeElementModel} chargeElement Referred to as the 'charge reference' in the UI, for example,
+ *  4.1.10. A charge version can have multiple charge elements, though each will have a different reference. Each
+ *  element can have multiple charge purposes and it's these that hold the abstraction period data
+ *
+ * @returns {Object} An object containing an `authorisedDays` and `billableDays` property
  */
 function go (chargePeriod, billingPeriod, chargeElement) {
   const { chargePurposes } = chargeElement
@@ -166,21 +164,18 @@ function _abstractionPeriods (referencePeriod, chargePurpose) {
  * @returns {number} the length of the period in days (inclusive)
  */
 function _calculateDays (abstractionOverlapPeriod) {
-  const DAY_IN_MILLISECONDS = (24 * 60 * 60 * 1000) // (24 hrs * 60 mins * 60 secs * 1000 msecs)
-
-  // difference in msecs
   const difference = abstractionOverlapPeriod.endDate.getTime() - abstractionOverlapPeriod.startDate.getTime()
 
   // ceil() always rounds up, even if the result is 1.1 (rounds to 2). We add 1 to make the calculation inclusive of
   // the last day
-  return Math.ceil(difference / DAY_IN_MILLISECONDS) + 1
+  return Math.ceil(difference / ONE_DAY_IN_MILLISECONDS) + 1
 }
 
 /**
  * Calculates the period that an abstraction period overlaps the reference period
  *
- * Before we can work out either the authorised or billable days, we first need to work out what part of the
- * abstraction period overlaps.
+ * Before we can work out either the authorised or billable days, we first need to work out what part of the abstraction
+ * period overlaps.
  *
  * The simplest way to look at this is that the overlapping period is the latest start date and the earliest end date.
  *
@@ -193,10 +188,11 @@ function _calculateDays (abstractionOverlapPeriod) {
  * - 01-NOV-2022 to 31-MAY-2023 - overlap is 01-NOV-2022 to 31-MAR-2023
  *
  * @param {Object} referencePeriod either the billing period or charge period
- * @param {*} abstractionPeriod a start and end date representing the abstraction period relative to the reference
+ * @param {Object} abstractionPeriod an object containing `startDate` and `endDate` date representing the abstraction
+ *  period relative to the reference
  *
  * @returns {Object} an object with a start and end date representing the part of the abstraction period that overlaps
- * the reference period
+ *  the reference period
  */
 function _calculateAbstractionOverlapPeriod (referencePeriod, abstractionPeriod) {
   const latestStartDateTimestamp = Math.max(abstractionPeriod.startDate, referencePeriod.startDate)
diff --git a/app/services/supplementary-billing/check-live-bill-run.service.js b/app/services/supplementary-billing/check-live-bill-run.service.js
index 671a56edd0..592d2a84f8 100644
--- a/app/services/supplementary-billing/check-live-bill-run.service.js
+++ b/app/services/supplementary-billing/check-live-bill-run.service.js
@@ -14,14 +14,14 @@ const LIVE_STATUSES = ['processing', 'ready', 'review', 'queued']
  *
  * We define "live" as having the status `processing`, `ready`, `review` or `queued`
  *
- * @param {*} regionId The id of the region to be checked
- * @param {*} financialYear The financial year to be checked
+ * @param {String} regionId The id of the region to be checked
+ * @param {Number} financialYear The financial year to be checked
  *
  * @returns {Boolean} Whether a "live" bill run exists
  */
 async function go (regionId, financialYear) {
   const numberOfLiveBillRuns = await BillingBatchModel.query()
-    .select('billing_batch_id')
+    .select(1)
     .where({
       regionId,
       toFinancialYearEnding: financialYear,
diff --git a/app/services/supplementary-billing/consolidate-date-ranges.service.js b/app/services/supplementary-billing/consolidate-date-ranges.service.js
index 89efa39211..28c4c8d85b 100644
--- a/app/services/supplementary-billing/consolidate-date-ranges.service.js
+++ b/app/services/supplementary-billing/consolidate-date-ranges.service.js
@@ -44,10 +44,9 @@
  *   { startDate: 2023-11-01, endDate: 2023-12-01 }  // Range 4 unchanged
  * ]
  *
- * @param {Array.<{startDate: Date, endDate: Date}>} dateRanges Array containing a series of date ranges to be
- *  consolidated, each of which is an Object containing startDate and endDate, both of which are Dates
+ * @param {{startDate: Date, endDate: Date}[]} dateRanges Array containing a series of date ranges to be consolidated.
  *
- * @returns {Array.<{startDate: Date, endDate: Date}>} An array of the consolidated date ranges
+ * @returns {{startDate: Date, endDate: Date}[]} An array of the consolidated date ranges
  */
 function go (dateRanges) {
   // We sort the date ranges by start date from earliest to latest to make life easier when consolidating them
@@ -92,9 +91,9 @@ function _consolidateDates (dateRanges) {
       return [...acc, previousRange]
     }
 
-    // If the current range's start date is on or earlier than the previous end date then the current range overlaps (starting
-    // the same day as the previous one ends counts as overlapping) so we add a new date range to our ongoing acc array,
-    // starting when the previous range starts and ending when the current range end
+    // If the current range's start date is on or earlier than the previous end date then the current range overlaps
+    // (starting the same day as the previous one ends counts as overlapping) so we add a new date range to our ongoing
+    // acc array, starting when the previous range starts and ending when the current range ends
     if (currentRange.startDate <= previousRange.endDate) {
       return [...acc, { startDate: previousRange.startDate, endDate: currentRange.endDate }]
     }
diff --git a/app/services/supplementary-billing/create-billing-batch-event.service.js b/app/services/supplementary-billing/create-billing-batch-event.service.js
index 5e2547d228..26d5056bfb 100644
--- a/app/services/supplementary-billing/create-billing-batch-event.service.js
+++ b/app/services/supplementary-billing/create-billing-batch-event.service.js
@@ -12,9 +12,9 @@ const GeneralLib = require('../../lib/general.lib.js')
 /**
  * Create an event for when a new bill run is initialised
  *
- * @param {module:BillingBatchModel} [billingBatch] An instance of `BillingBatchModel` representing the initialised
- *   billing batch
- * @param {String} [issuer] The email address of the user triggering the event
+ * @param {module:BillingBatchModel} billingBatch An instance of `BillingBatchModel` representing the initialised
+ *  billing batch
+ * @param {String} issuer The email address of the user triggering the event
  *
  * @returns {Object} The newly created event record
  */
diff --git a/app/services/supplementary-billing/create-billing-batch.service.js b/app/services/supplementary-billing/create-billing-batch.service.js
index 62c138726c..d9f67dbb72 100644
--- a/app/services/supplementary-billing/create-billing-batch.service.js
+++ b/app/services/supplementary-billing/create-billing-batch.service.js
@@ -13,13 +13,13 @@ const BillingBatchModel = require('../../models/water/billing-batch.model.js')
  * @param {Object} regionId The regionId for the selected region
  * @param {Object} billingPeriod The billing period in the format { startDate: 2022-04-01, endDate: 2023-03-31 }
  * @param {Object} options Optional params to be overridden
- * @param {string} [options.batchType=supplementary] The type of billing batch to create. Defaults to 'supplementary'
- * @param {string} [options.scheme=sroc] The applicable charging scheme. Defaults to 'sroc'
- * @param {string} [options.source=wrls] Where the billing batch originated from. Records imported from NALD have the
+ * @param {String} [options.batchType=supplementary] The type of billing batch to create. Defaults to 'supplementary'
+ * @param {String} [options.scheme=sroc] The applicable charging scheme. Defaults to 'sroc'
+ * @param {String} [options.source=wrls] Where the billing batch originated from. Records imported from NALD have the
  *  source 'nald'. Those created in the service use 'wrls'. Defaults to 'wrls'
- * @param {string} [options.externalId=null] The id of the bill run as created in the Charging Module
- * @param {string} [options.status=queued] The status that the bill run should be created with
- * @param {number} [options.errorCode=null] Numeric error code
+ * @param {String} [options.externalId=null] The id of the bill run as created in the Charging Module
+ * @param {String} [options.status=queued] The status that the bill run should be created with
+ * @param {Number} [options.errorCode=null] Numeric error code
  *
  * @returns {module:BillingBatchModel} The newly created billing batch instance with the `.region` property populated
  */
diff --git a/app/services/supplementary-billing/determine-charge-period.service.js b/app/services/supplementary-billing/determine-charge-period.service.js
index 61b25a5a9f..5c8ad5ba9b 100644
--- a/app/services/supplementary-billing/determine-charge-period.service.js
+++ b/app/services/supplementary-billing/determine-charge-period.service.js
@@ -14,10 +14,10 @@
  *
  * > Charge versions may not have an end date; in this case, we simply use the financial year end date.
  *
- * @param {module:ChargeVersionModel} chargeVersion the charge version being processed for billing
- * @param {number} financialYearEnding the year the financial billing period ends
+ * @param {module:ChargeVersionModel} chargeVersion The charge version being processed for billing
+ * @param {Number} financialYearEnding The year the financial billing period ends
  *
- * @returns {Object} the start and end date of the calculated charge period
+ * @returns {{startDate: Date, endDate: Date}} The start and end date of the calculated charge period
  */
 function go (chargeVersion, financialYearEnding) {
   const financialYearStartDate = new Date(financialYearEnding - 1, 3, 1)
diff --git a/app/services/supplementary-billing/determine-minimum-charge.service.js b/app/services/supplementary-billing/determine-minimum-charge.service.js
index 015eae0f23..fd744a1751 100644
--- a/app/services/supplementary-billing/determine-minimum-charge.service.js
+++ b/app/services/supplementary-billing/determine-minimum-charge.service.js
@@ -10,15 +10,15 @@ const DetermineChargePeriodService = require('./determine-charge-period.service.
 /**
  * Checks if minimum charge applies to a charge version for the given billing period
  *
- * If the charge version's start date matches the start of the charging period, and the reason for its creation
- * is flagged as triggering a minimum charge this service will return true.
+ * If the charge version's start date matches the start of the charging period, and the reason for its creation is
+ * flagged as triggering a minimum charge this service will return true.
  *
  * If either of those tests is false then the service will return false.
  *
- * @param {module:ChargeVersionModel} chargeVersion the charge version being checked for minimum charge
- * @param {number} financialYearEnding the year the financial billing period ends
+ * @param {module:ChargeVersionModel} chargeVersion The charge version being checked for minimum charge
+ * @param {Number} financialYearEnding The year the financial billing period ends
  *
- * @returns {boolean} true if minimum charge applies else false
+ * @returns {Boolean} true if minimum charge applies else false
  */
 function go (chargeVersion, financialYearEnding) {
   const chargePeriod = DetermineChargePeriodService.go(chargeVersion, financialYearEnding)
@@ -30,7 +30,6 @@ function go (chargeVersion, financialYearEnding) {
   const triggersMinimumCharge = chargeVersion.changeReason?.triggersMinimumCharge ?? false
   const isFirstChargeOnNewLicence = isSharedStartDate && triggersMinimumCharge
 
-  // TODO: confirm whether legacy code is correct when it says return true if charge period starts on first april
   return isFirstChargeOnNewLicence
 }
 
diff --git a/app/services/supplementary-billing/fetch-charge-versions.service.js b/app/services/supplementary-billing/fetch-charge-versions.service.js
index b936998bcd..512abb32ee 100644
--- a/app/services/supplementary-billing/fetch-charge-versions.service.js
+++ b/app/services/supplementary-billing/fetch-charge-versions.service.js
@@ -14,10 +14,10 @@ const ChargeVersionWorkflow = require('../../models/water/charge-version-workflo
  * Fetch all SROC charge versions linked to licences flagged for supplementary billing that are in the period being
  * billed
  *
- * @param {string} regionId UUID of the region being billed that the licences must be linked to
+ * @param {String} regionId UUID of the region being billed that the licences must be linked to
  * @param {Object} billingPeriod Object with a `startDate` and `endDate` property representing the period being billed
  *
- * @returns {Object[]} an array of matching charge versions
+ * @returns {Object[]} An array of matching charge versions
  */
 async function go (regionId, billingPeriod) {
   const chargeVersions = await _fetch(regionId, billingPeriod)
diff --git a/app/services/supplementary-billing/fetch-previous-billing-transactions.service.js b/app/services/supplementary-billing/fetch-previous-billing-transactions.service.js
index 6e82c8f025..f63f6a6c77 100644
--- a/app/services/supplementary-billing/fetch-previous-billing-transactions.service.js
+++ b/app/services/supplementary-billing/fetch-previous-billing-transactions.service.js
@@ -8,6 +8,18 @@
 
 const { db } = require('../../../db/db.js')
 
+/**
+ * Fetches the previously billed transactions that match the invoice, licence and year provided, removing any debits
+ * which are cancelled out by previous credits.
+ *
+ * @param {Object} billingInvoice A generated billing invoice that identifies the invoice account ID we need to match
+ *  against
+ * @param {Object} billingInvoiceLicence A generated billing invoice licence that identifies the licence we need to
+ *  match against
+ * @param {Number} financialYearEnding The year the financial billing period ends that we need to match against
+ *
+ * @returns {Object} The resulting matched billing transactions
+ */
 async function go (billingInvoice, billingInvoiceLicence, financialYearEnding) {
   const billingTransactions = await _fetch(
     billingInvoiceLicence.licenceId,
diff --git a/app/services/supplementary-billing/fetch-region.service.js b/app/services/supplementary-billing/fetch-region.service.js
index 0af8a81f95..2a09ac7197 100644
--- a/app/services/supplementary-billing/fetch-region.service.js
+++ b/app/services/supplementary-billing/fetch-region.service.js
@@ -13,8 +13,8 @@ const RegionModel = require('../../models/water/region.model.js')
  * This is a temporary service to help us confirm we are selecting the correct data to use when creating a
  * supplementary bill run. Its primary aim is to meet the acceptance criteria defined in WATER-3787.
  *
- * @param {string} naldRegionId The NALD region ID (a number between 1 to 9, 9 being the test region) for the region
- * to find
+ * @param {String} naldRegionId The NALD region ID (a number between 1 to 9, 9 being the test region) for the region
+ *  to find
  *
  * @returns {Object} Instance of `RegionModel` with the matching NALD Region ID
  */
diff --git a/app/services/supplementary-billing/generate-billing-invoice-licence.service.js b/app/services/supplementary-billing/generate-billing-invoice-licence.service.js
index 144d57701b..458c00fd27 100644
--- a/app/services/supplementary-billing/generate-billing-invoice-licence.service.js
+++ b/app/services/supplementary-billing/generate-billing-invoice-licence.service.js
@@ -10,16 +10,14 @@ const { randomUUID } = require('crypto')
 /**
  * Return either a new billing invoice licence object ready for persisting or an existing one if it exists
  *
- * This first checks whether a billing invoice licence with the same invoice and licence ID exists in
- * `generatedBillingInvoiceLicences`. The calling service is expected to provide and keep track of this variable
- * between calls. If it does, it returns that instance along with the original array unchanged.
+ * This first checks whether the billing invoice id and licence id of `currentBillingInvoiceLicence` match the ones
+ * passed to this service. If they do, we return that instance.
  *
- * If it doesn't, we generate a new instance and create a new array, based on the one provided plus our new instance.
- * We then return the instance and the new array as the result.
+ * If they don't, we generate a new instance and return it.
  *
- * For context, this is all to avoid creating `billing_invoice` and `billing_invoice_licence` records unnecessarily.
- * The legacy service will create them first, then determine if there are any transactions to be billed. If there
- * aren't, it then has to go back and delete the records it created.
+ * For context, this is all to avoid creating `billing_invoice` and `billing_invoice_licence` records unnecessarily. The
+ * legacy service will create them first, then determine if there are any transactions to be billed. If there aren't, it
+ * then has to go back and delete the records it created.
  *
  * Our intent is to only call the DB when we have records that need persisting. So, we start at the transaction level
  * and only persist `billing_invoice` and `billing_invoice_licence` records that are linked to billable transactions.
@@ -27,13 +25,12 @@ const { randomUUID } = require('crypto')
  * licence data in memory along with ID's, and use this service to provide the right record when persisting the
  * transaction.
  *
- * @param {Object[]} generatedBillingInvoiceLicences An array of previously generated billing invoice licence objects
- * @param {string} billingInvoiceId UUID of the billing invoice this billing invoice licence will be linked to if
- * persisted
- * @param {module:LicenceModel} licence the licence this billing invoice licence will be linked to
+ * @param {module:billingInvoiceLicence} currentBillingInvoiceLicence A billing invoice licence object
+ * @param {String} billingInvoiceId UUID of the billing invoice this billing invoice licence will be linked to if
+ *  persisted
+ * @param {module:LicenceModel} licence The licence this billing invoice licence will be linked to
  *
- * @returns {Object} A result object containing either the found or generated billing invoice licence object, and an
- * array of generated billing invoice licences which includes the one being returned
+ * @returns {Object} The current or newly-generated billing invoice licence object
  */
 function go (currentBillingInvoiceLicence, billingInvoiceId, licence) {
   if (
diff --git a/app/services/supplementary-billing/generate-billing-invoice.service.js b/app/services/supplementary-billing/generate-billing-invoice.service.js
index c74f6e1251..f41f96fa57 100644
--- a/app/services/supplementary-billing/generate-billing-invoice.service.js
+++ b/app/services/supplementary-billing/generate-billing-invoice.service.js
@@ -12,12 +12,10 @@ const InvoiceAccountModel = require('../../models/crm-v2/invoice-account.model.j
 /**
  * Return either a new billing invoice object ready for persisting or an existing one if it exists
  *
- * This first checks whether a billing invoice with the same invoice account ID exists in
- * `generatedBillingInvoices`. The calling service is expected to provide and keep track of this variable between
- * between calls. If it does, it returns that instance along with the original array unchanged.
+ * This first checks whether the invoice account ID of `currentBillingInvoice` matches the one passed to this service.
+ * If it does, we return that instance.
  *
- * If it doesn't, we generate a new instance and create a new array, based on the one provided plus our new instance.
- * We then return the instance and the new array as the result.
+ * If it doesn't, we generate a new instance and return it.
  *
  * For context, this is all to avoid creating `billing_invoice` and `billing_invoice_licence` records unnecessarily.
  * The legacy service will create them first, then determine if there are any transactions to be billed. If there
@@ -29,13 +27,12 @@ const InvoiceAccountModel = require('../../models/crm-v2/invoice-account.model.j
  * licence data in memory along with ID's, and use this service to provide the right record when persisting the
  * transaction.
  *
- * @param {Object[]} generatedBillingInvoices An array of previously generated billing invoice objects
- * @param {*} invoiceAccountId UUID of the invoice account this billing invoice will be linked to if persisted
- * @param {*} billingBatchId UUID of the billing batch this billing invoice will be linked to if persisted
- * @param {*} financialYearEnding a value that must exist in the persisted record
+ * @param {module:BillingInvoiceModel} currentBillingInvoice A billing invoice object
+ * @param {String} invoiceAccountId UUID of the invoice account this billing invoice will be linked to if persisted
+ * @param {String} billingBatchId UUID of the billing batch this billing invoice will be linked to if persisted
+ * @param {Number} financialYearEnding A value that must exist in the persisted record
  *
- * @returns {Object} A result object containing either the found or generated billing invoice object, and an array of
- * generated billing invoices which includes the one being returned
+ * @returns {Object} The current or newly-generated billing invoice object
  */
 async function go (currentBillingInvoice, invoiceAccountId, billingBatchId, financialYearEnding) {
   if (currentBillingInvoice?.invoiceAccountId === invoiceAccountId) {
diff --git a/app/services/supplementary-billing/generate-billing-transactions.service.js b/app/services/supplementary-billing/generate-billing-transactions.service.js
index 605a1f3bb6..6989904925 100644
--- a/app/services/supplementary-billing/generate-billing-transactions.service.js
+++ b/app/services/supplementary-billing/generate-billing-transactions.service.js
@@ -24,11 +24,11 @@ const CalculateAuthorisedAndBillableDaysServiceService = require('./calculate-au
  * They will then be returned in an array for further processing before being persisted to the DB as
  * `billing_transactions`.
  *
- * @param {Object} chargeElement the charge element the transaction generated from
- * @param {Object} billingPeriod a start and end date representing the billing period for the billing batch
- * @param {Object} chargePeriod a start and end date representing the charge period for the charge version
- * @param {boolean} isNewLicence whether the charge version is linked to a new licence
- * @param {boolean} isWaterUndertaker whether the charge version is linked to a water undertaker licence
+ * @param {Object} chargeElement The charge element the transaction generated from
+ * @param {Object} billingPeriod A start and end date representing the billing period for the billing batch
+ * @param {Object} chargePeriod A start and end date representing the charge period for the charge version
+ * @param {Boolean} isNewLicence Whether the charge version is linked to a new licence
+ * @param {Boolean} isWaterUndertaker Whether the charge version is linked to a water undertaker licence
  *
  * @returns {Object[]} an array of 0, 1 or 2 transaction objects
  */
@@ -64,6 +64,10 @@ function go (chargeElement, billingPeriod, chargePeriod, isNewLicence, isWaterUn
   return billingTransactions
 }
 
+/**
+ * Generates a compensation transaction by taking a standard transaction and overwriting it with the supplied billing id
+ * and the correct charge type and description for a compensation charge.
+ */
 function _compensationTransaction (billingTransactionId, standardTransaction) {
   return {
     ...standardTransaction,
@@ -103,6 +107,9 @@ function _generatePurposes (chargeElement) {
   return JSON.stringify(jsonChargePurposes)
 }
 
+/**
+ * Generates a standard transaction based on the supplied data, along with some default fields (eg. status)
+ */
 function _standardTransaction (
   billingTransactionId,
   authorisedDays,
diff --git a/app/services/supplementary-billing/handle-errored-billing-batch.service.js b/app/services/supplementary-billing/handle-errored-billing-batch.service.js
index dd394d3165..b481f1a3ce 100644
--- a/app/services/supplementary-billing/handle-errored-billing-batch.service.js
+++ b/app/services/supplementary-billing/handle-errored-billing-batch.service.js
@@ -16,8 +16,8 @@ const BillingBatchModel = require('../../models/water/billing-batch.model.js')
  * Note that although this is async we would generally not call it asyncronously as the intent is you can call it and
  * continue with whatever error logging is required
  *
- * @param {string} billingBatchId UUID of the billing batch to be marked with `error` status
- * @param {number} [errorCode] Numeric error code as defined in BillingBatchModel. Defaults to `null`
+ * @param {String} billingBatchId UUID of the billing batch to be marked with `error` status
+ * @param {Number} [errorCode] Numeric error code as defined in BillingBatchModel. Defaults to `null`
  */
 async function go (billingBatchId, errorCode = null) {
   try {
diff --git a/app/services/supplementary-billing/process-billing-batch.service.js b/app/services/supplementary-billing/process-billing-batch.service.js
index 7150eda33d..77fadcf983 100644
--- a/app/services/supplementary-billing/process-billing-batch.service.js
+++ b/app/services/supplementary-billing/process-billing-batch.service.js
@@ -29,7 +29,7 @@ const ProcessBillingTransactionsService = require('./process-billing-transaction
  * TODO: Currently a placeholder service. Proper implementation is coming
  *
  * @param {module:BillingBatchModel} billingBatch The newly created bill batch we need to process
- * @param {Object} billingPeriod an object representing the financial year the transaction is for
+ * @param {Object} billingPeriod An object representing the financial year the transaction is for
  */
 async function go (billingBatch, billingPeriod) {
   const { billingBatchId } = billingBatch
@@ -94,15 +94,15 @@ async function go (billingBatch, billingPeriod) {
 }
 
 /**
-   * Log the time taken to process the billing batch
-   *
-   * If `notifier` is not set then it will do nothing. If it is set this will get the current time and then calculate the
-   * difference from `startTime`. This and the `billRunId` are then used to generate a log message.
-   *
-   * @param {string} billingBatchId Id of the billing batch currently being 'processed'
-   * @param {BigInt} startTime The time the generate process kicked off. It is expected to be the result of a call to
-   * `process.hrtime.bigint()`
-   */
+  * Log the time taken to process the billing batch
+  *
+  * If `notifier` is not set then it will do nothing. If it is set this will get the current time and then calculate the
+  * difference from `startTime`. This and the `billRunId` are then used to generate a log message.
+  *
+  * @param {string} billingBatchId Id of the billing batch currently being 'processed'
+  * @param {BigInt} startTime The time the generate process kicked off. It is expected to be the result of a call to
+  * `process.hrtime.bigint()`
+  */
 function _calculateAndLogTime (billingBatchId, startTime) {
   const endTime = process.hrtime.bigint()
   const timeTakenNs = endTime - startTime
diff --git a/app/services/supplementary-billing/process-billing-transactions.service.js b/app/services/supplementary-billing/process-billing-transactions.service.js
index e193431ade..ef0db3ad20 100644
--- a/app/services/supplementary-billing/process-billing-transactions.service.js
+++ b/app/services/supplementary-billing/process-billing-transactions.service.js
@@ -1,8 +1,31 @@
 'use strict'
 
+/**
+ * Fetches the matching debit billing transactions from a previous billing batch and reverses them as credits; removes
+ * any which would be cancelled out by the supplied calculated debit transactions; combines the remaining transactions
+ * and returns them all
+ * @module ProcessBillingTransactionsService
+ */
+
 const FetchPreviousBillingTransactionsService = require('./fetch-previous-billing-transactions.service.js')
 const ReverseBillingTransactionsService = require('./reverse-billing-transactions.service.js')
 
+/**
+ * Fetches debit-only billing transactions from the previous billing batch for the invoice account and licence provided
+ * and reverses them as credits. These credits are compared with the supplied calculated debit transactions (ie. debit
+ * transactions which are to be sent to the Charging Module) and any matching pairs of transactions which would cancel
+ * each other out are removed. Any remaining reversed credits and calculated debits are returned.
+ *
+ * @param {Object[]} calculatedTransactions The calculated transactions to be processed
+ * @param {Object} billingInvoice A generated billing invoice that identifies the invoice account ID we need to match
+ *  against
+ * @param {Object} billingInvoiceLicence A generated billing invoice licence that identifies the licence we need to
+ *  match against
+ * @param {Object} billingPeriod Object with a `startDate` and `endDate` property representing the period being billed
+ *
+ * @returns {Object[]} An array of the remaining calculated transactions (ie. those which were not cancelled out by a
+ *  previous matching credit)
+ */
 async function go (calculatedTransactions, billingInvoice, billingInvoiceLicence, billingPeriod) {
   const previousTransactions = await _fetchPreviousTransactions(billingInvoice, billingInvoiceLicence, billingPeriod)
 
@@ -15,12 +38,19 @@ async function go (calculatedTransactions, billingInvoice, billingInvoiceLicence
   return _cleanseTransactions(calculatedTransactions, reversedTransactions)
 }
 
+/**
+ * Takes a single calculated debit transaction and checks to see if the provided array of reversed (credit) transactions
+ * contains a transaction that will cancel it out, returning `true` or `false` to indicate if it does or doesn't. Since
+ * the calculated debit transactions have not yet been sent to the Charging Module, we look at `chargeType`,
+ * `chargeCategoryCode` and `billableDays` as any given combination of these will always result in the same value coming
+ * back from the Charging Module.
+ *
+ * NOTE: This function will mutate the provided array of reversed transactions if one of the transactions in it will
+ * cancel the calculated transaction; in this case, we remove the reversed transaction from the array as it can only
+ * cancel one calculated transaction.
+ */
 function _cancelCalculatedTransaction (calculatedTransaction, reversedTransactions) {
   const result = reversedTransactions.findIndex((reversedTransaction) => {
-    // Example of the things we are comparing
-    // - chargeType - standard or compensation
-    // - chargeCategory - 4.10.1
-    // - billableDays - 215
     return reversedTransaction.chargeType === calculatedTransaction.chargeType &&
       reversedTransaction.chargeCategoryCode === calculatedTransaction.chargeCategoryCode &&
       reversedTransaction.billableDays === calculatedTransaction.billableDays
@@ -38,17 +68,23 @@ function _cancelCalculatedTransaction (calculatedTransaction, reversedTransactio
 /**
  * Remove any "cancelling pairs" of transaction lines. We define a "cancelling pair" as a pair of transactions belonging
  * to the same billing invoice licence which would send the same data to the Charging Module (and therefore return the
- * same values) but with opposing credit flags -- in other words, a credit and a debit which cancel each other out.
+ * same values) but with opposing credit flags -- in other words, a credit and a debit which cancel each other out. All
+ * remaining transactions (both calculated transactions and reverse transactions) are returned.
  */
 function _cleanseTransactions (calculatedTransactions, reverseTransactions) {
   const cleansedTransactionLines = []
 
+  // Iterate over each calculated transaction to see if a transaction in the reverse transactions would form a
+  // "cancelling pair" with it. If not then add the unpaired calculated transaction to our array of cleansed transaction
+  // lines. Note that `reverseTransactions` will be mutated to remove any reverse transactions which form a cancelling
+  // pair.
   for (const calculatedTransactionLine of calculatedTransactions) {
     if (!_cancelCalculatedTransaction(calculatedTransactionLine, reverseTransactions)) {
       cleansedTransactionLines.push(calculatedTransactionLine)
     }
   }
 
+  // Add the remaining reverse transactions (ie. those which didn't form a cancelling pair)
   cleansedTransactionLines.push(...reverseTransactions)
 
   return cleansedTransactionLines
diff --git a/app/services/supplementary-billing/process-previous-billing-transactions.service.js b/app/services/supplementary-billing/process-previous-billing-transactions.service.js
deleted file mode 100644
index 14bd906d43..0000000000
--- a/app/services/supplementary-billing/process-previous-billing-transactions.service.js
+++ /dev/null
@@ -1,42 +0,0 @@
-'use strict'
-
-/**
- * Fetches the matching debit billing transactions from a previous billing batch and reverses them as credits
- * @module ProcessPreviousBillingTransactionsService
- */
-
-const FetchPreviousBillingTransactionsService = require('./fetch-previous-billing-transactions.service.js')
-const ReverseBillingTransactionsService = require('./reverse-billing-transactions.service.js')
-
-/**
- * Fetches debit-only billing transactions from the previous billing batch for the invoice account and licence provided
- * then reverses them as credits
- *
- * @param {Object} billingInvoice A generated billing invoice that identifies the invoice account ID we need to match
- * against
- * @param {Object} billingInvoiceLicence A generated billing invoice licence  that identifies the licence we need to
- * match against. Also, has the billing invoice licence ID we'll be linked our reversed transactions to
- * @param {Object} billingPeriod Object with a `startDate` and `endDate` property representing the period being billed
- *
- * @returns {Object[]} an array of matching Billing Transaction objects with new transaction IDs, the billing invoice
- * licence ID set to that passed in, and the `isCredit:` reversed to true
- */
-async function go (billingInvoice, billingInvoiceLicence, billingPeriod) {
-  const previousTransactions = await _fetchPreviousTransactions(billingInvoice, billingInvoiceLicence, billingPeriod)
-
-  const reversedTransactions = ReverseBillingTransactionsService.go(previousTransactions, billingInvoiceLicence)
-
-  return reversedTransactions
-}
-
-async function _fetchPreviousTransactions (billingInvoice, billingInvoiceLicence, billingPeriod) {
-  const financialYearEnding = billingPeriod.endDate.getFullYear()
-
-  const transactions = await FetchPreviousBillingTransactionsService.go(billingInvoice, billingInvoiceLicence, financialYearEnding)
-
-  return transactions
-}
-
-module.exports = {
-  go
-}
diff --git a/app/services/supplementary-billing/reverse-billing-transactions.service.js b/app/services/supplementary-billing/reverse-billing-transactions.service.js
index 4f9d9c807c..6b3dd417ae 100644
--- a/app/services/supplementary-billing/reverse-billing-transactions.service.js
+++ b/app/services/supplementary-billing/reverse-billing-transactions.service.js
@@ -15,11 +15,11 @@ const { randomUUID } = require('crypto')
  * will reverse the original transactions, with their billing invoice licence id set to the id of the supplied billing
  * invoice licence.
  *
- * @param {Array[module:BillingTransactionModel]} transactions Array of transactions to be reversed
+ * @param {module:BillingTransactionModel[]} transactions Array of transactions to be reversed
  * @param {module:BillingInvoiceLicenceModel} billingInvoiceLicence The billing invoice licence these transactions are
  *  intended to be added to
  *
- * @returns {Array[Object]} Array of reversing transactions with `billingInvoiceLicenceId` set to the id of the supplied
+ * @returns {Object[]} Array of reversing transactions with `billingInvoiceLicenceId` set to the id of the supplied
  *  `billingInvoiceLicence`
  */
 function go (transactions, billingInvoiceLicence) {
diff --git a/test/controllers/check/supplementary.controller.test.js b/test/controllers/check/supplementary.controller.test.js
deleted file mode 100644
index 15a63a0bc7..0000000000
--- a/test/controllers/check/supplementary.controller.test.js
+++ /dev/null
@@ -1,48 +0,0 @@
-'use strict'
-
-// Test framework dependencies
-const Lab = require('@hapi/lab')
-const Code = require('@hapi/code')
-const Sinon = require('sinon')
-
-const { describe, it, beforeEach, after } = exports.lab = Lab.script()
-const { expect } = Code
-
-// Things we need to stub
-const SupplementaryDataService = require('../../../app/services/check/supplementary-data.service.js')
-
-// For running our service
-const { init } = require('../../../app/server.js')
-
-describe('Supplementary controller', () => {
-  let server
-
-  beforeEach(async () => {
-    server = await init()
-  })
-
-  after(() => {
-    Sinon.restore()
-  })
-
-  describe('GET /check/supplementary', () => {
-    const options = {
-      method: 'GET',
-      url: '/check/supplementary?region=9'
-    }
-
-    let response
-
-    beforeEach(async () => {
-      Sinon.stub(SupplementaryDataService, 'go').resolves({ billingPeriods: [], licences: [], chargeVersions: [] })
-
-      response = await server.inject(options)
-    })
-
-    describe('when the request is valid', () => {
-      it('returns success status 200', async () => {
-        expect(response.statusCode).to.equal(200)
-      })
-    })
-  })
-})
diff --git a/test/presenters/check/supplementary-data.presenter.test.js b/test/presenters/check/supplementary-data.presenter.test.js
deleted file mode 100644
index 28966ae11b..0000000000
--- a/test/presenters/check/supplementary-data.presenter.test.js
+++ /dev/null
@@ -1,83 +0,0 @@
-'use strict'
-
-// Test framework dependencies
-const Lab = require('@hapi/lab')
-const Code = require('@hapi/code')
-
-const { describe, it, beforeEach } = exports.lab = Lab.script()
-const { expect } = Code
-
-// Thing under test
-const SupplementaryDataPresenter = require('../../../app/presenters/check/supplementary-data.presenter.js')
-
-describe('Supplementary presenter', () => {
-  let data
-
-  describe('when there are results', () => {
-    beforeEach(() => {
-      data = {
-        billingPeriods: [
-          {
-            startDate: new Date(2022, 3, 1), // 2022-04-01 - Months are zero indexed
-            endDate: new Date(2023, 2, 31)
-          }
-        ],
-        chargeVersions: [
-          {
-            chargeVersionId: '6a472535-145c-4170-ab59-f555783fa6e7',
-            scheme: 'sroc',
-            startDate: new Date(2022, 4, 1),
-            endDate: null,
-            licence: {
-              licenceId: 'f1288f6c-8503-4dc1-b114-75c408a14bd0',
-              licenceRef: 'AT/SROC/SUPB/01'
-            },
-            chargeElements: [
-              {
-                chargeElementId: '0382824f-2b17-4294-aa57-c5fe5749960f',
-                chargePurposes: [
-                  {
-                    chargePurposeId: 'ffcb7d57-6148-4ee7-bc95-9de23c0cdc39',
-                    abstractionPeriodStartDay: 1,
-                    abstractionPeriodStartMonth: 4,
-                    abstractionPeriodEndDay: 31,
-                    abstractionPeriodEndMonth: 3
-                  }
-                ],
-                billingChargeCategory: {
-                  reference: '4.2.1'
-                }
-              }
-            ]
-          }
-        ]
-      }
-    })
-
-    it('correctly presents the data', () => {
-      const result = SupplementaryDataPresenter.go(data)
-
-      expect(result.billingPeriods).to.have.length(1)
-      expect(result.billingPeriods[0]).to.equal(data.billingPeriods[0])
-
-      expect(result.chargeVersions).to.have.length(1)
-      expect(result.chargeVersions[0]).to.equal(data.chargeVersions[0])
-    })
-  })
-
-  describe('when there are no results', () => {
-    beforeEach(() => {
-      data = {
-        billingPeriods: [],
-        chargeVersions: []
-      }
-    })
-
-    it('correctly presents the data', () => {
-      const result = SupplementaryDataPresenter.go(data)
-
-      expect(result.billingPeriods).to.be.empty()
-      expect(result.chargeVersions).to.be.empty()
-    })
-  })
-})
diff --git a/test/services/check/supplementary-data.service.test.js b/test/services/check/supplementary-data.service.test.js
deleted file mode 100644
index c220f486ee..0000000000
--- a/test/services/check/supplementary-data.service.test.js
+++ /dev/null
@@ -1,82 +0,0 @@
-'use strict'
-
-// Test framework dependencies
-const Lab = require('@hapi/lab')
-const Code = require('@hapi/code')
-const Sinon = require('sinon')
-
-const { describe, it, beforeEach, afterEach } = exports.lab = Lab.script()
-const { expect } = Code
-
-// Things we need to stub
-const BillingPeriodService = require('../../../app/services/supplementary-billing/billing-period.service.js')
-const FetchChargeVersionsService = require('../../../app/services/supplementary-billing/fetch-charge-versions.service.js')
-const FetchRegionService = require('../../../app/services/supplementary-billing/fetch-region.service.js')
-
-// Thing under test
-const SupplementaryDataService = require('../../../app/services/check/supplementary-data.service.js')
-
-describe('Supplementary service', () => {
-  const naldRegionId = 9
-  const currentBillingPeriod = {
-    startDate: new Date('2022-04-01'),
-    endDate: new Date('2023-03-31')
-  }
-
-  beforeEach(async () => {
-    Sinon.stub(BillingPeriodService, 'go').returns([currentBillingPeriod])
-    Sinon.stub(FetchRegionService, 'go').resolves({ regionId: 'bd114474-790f-4470-8ba4-7b0cc9c225d7' })
-  })
-
-  afterEach(() => {
-    Sinon.restore()
-  })
-
-  describe('the response for billing periods', () => {
-    beforeEach(async () => {
-      Sinon.stub(FetchChargeVersionsService, 'go').resolves([])
-    })
-
-    it('always includes the current billing period', async () => {
-      const result = await SupplementaryDataService.go(naldRegionId)
-
-      expect(result.billingPeriods).to.have.length(1)
-      expect(result.billingPeriods[0]).to.equal(currentBillingPeriod)
-    })
-  })
-
-  describe('the response for charge versions', () => {
-    describe('when there are charge versions for supplementary billing', () => {
-      const testRecords = [{
-        chargeVersionId: '4b5cbe04-a0e2-468c-909e-1e2d93810ba8',
-        scheme: 'sroc',
-        endDate: null,
-        licenceId: '2627a306-23a3-432f-9c71-a71663888285',
-        licenceRef: 'AT/SROC/SUPB/01'
-      }]
-
-      beforeEach(async () => {
-        Sinon.stub(FetchChargeVersionsService, 'go').resolves(testRecords)
-      })
-
-      it('returns the matching charge versions', async () => {
-        const result = await SupplementaryDataService.go(naldRegionId)
-
-        expect(result.chargeVersions).to.have.length(1)
-        expect(result.chargeVersions[0].chargeVersionId).to.equal(testRecords[0].chargeVersionId)
-      })
-    })
-
-    describe('When there are no charge versions for supplementary billing', () => {
-      beforeEach(async () => {
-        Sinon.stub(FetchChargeVersionsService, 'go').resolves([])
-      })
-
-      it('returns no results', async () => {
-        const result = await SupplementaryDataService.go(naldRegionId)
-
-        expect(result.chargeVersions).to.be.empty()
-      })
-    })
-  })
-})
diff --git a/test/services/supplementary-billing/process-previous-billing-transactions.service.test.js b/test/services/supplementary-billing/process-previous-billing-transactions.service.test.js
deleted file mode 100644
index 02f133a64e..0000000000
--- a/test/services/supplementary-billing/process-previous-billing-transactions.service.test.js
+++ /dev/null
@@ -1,76 +0,0 @@
-'use strict'
-
-// Test framework dependencies
-const Lab = require('@hapi/lab')
-const Code = require('@hapi/code')
-const Sinon = require('sinon')
-
-const { describe, it, beforeEach, afterEach } = exports.lab = Lab.script()
-const { expect } = Code
-
-// Things we need to stub
-const FetchPreviousBillingTransactionsService = require('../../../app/services/supplementary-billing/fetch-previous-billing-transactions.service.js')
-
-// Thing under test
-const ProcessPreviousBillingTransactionsService = require('../../../app/services/supplementary-billing/process-previous-billing-transactions.service.js')
-
-describe('Process previous billing transactions service', () => {
-  const billingInvoice = { billingInvoiceId: 'a56ef6d9-370a-4224-b6ec-0fca8bfa4d1f' }
-  const billingInvoiceLicence = { billingInvoiceLicenceId: '110ab2e2-6076-4d5a-a56f-b17a048eb269' }
-
-  const billingPeriod = {
-    startDate: new Date('2022-04-01'),
-    endDate: new Date('2023-03-31')
-  }
-
-  const previousTransaction = {
-    billingTransactionId: '63742bee-cb1b-44f1-86f6-c7d546f59c88',
-    billingInvoiceLicenceId: '110ab2e2-6076-4d5a-a56f-b17a048eb269',
-    isCredit: false,
-    status: 'candidate',
-    chargeType: 'standard',
-    chargeCategoryCode: '5.11.2',
-    billableDays: 265,
-    purposes: []
-  }
-
-  afterEach(() => {
-    Sinon.restore()
-  })
-
-  describe('when the billing invoice, licence and period', () => {
-    describe('match to transactions on a previous billing batch', () => {
-      beforeEach(() => {
-        Sinon.stub(FetchPreviousBillingTransactionsService, 'go').resolves([previousTransaction])
-      })
-
-      it('returns the debits reversed as credits with new Ids', async () => {
-        const result = await ProcessPreviousBillingTransactionsService.go(
-          billingInvoice,
-          billingInvoiceLicence,
-          billingPeriod
-        )
-
-        expect(result).to.have.length(1)
-        expect(result[0].billingTransactionId).not.to.equal(previousTransaction.billingTransactionId)
-        expect(result[0].isCredit).not.to.equal(previousTransaction.isCredit)
-      })
-    })
-
-    describe('do not match to transactions on a previous billing batch', () => {
-      beforeEach(() => {
-        Sinon.stub(FetchPreviousBillingTransactionsService, 'go').resolves([])
-      })
-
-      it('returns an empty array', async () => {
-        const result = await ProcessPreviousBillingTransactionsService.go(
-          billingInvoice,
-          billingInvoiceLicence,
-          billingPeriod
-        )
-
-        expect(result).to.be.empty()
-      })
-    })
-  })
-})