diff --git a/plugins/optimization-detective/class-od-url-metric.php b/plugins/optimization-detective/class-od-url-metric.php
index c565b1595..a9ba604de 100644
--- a/plugins/optimization-detective/class-od-url-metric.php
+++ b/plugins/optimization-detective/class-od-url-metric.php
@@ -38,7 +38,7 @@
  *                            }
  * @phpstan-type Data         array{
  *                                uuid: non-empty-string,
- *                                eTag?: string,
+ *                                etag?: string,
  *                                url: non-empty-string,
  *                                timestamp: float,
  *                                viewport: ViewportRect,
@@ -156,7 +156,7 @@ public function set_group( OD_URL_Metric_Group $group ): void {
 	 * Gets JSON schema for URL Metric.
 	 *
 	 * @since 0.1.0
-	 * @since n.e.x.t Added the 'eTag' property to the schema.
+	 * @since n.e.x.t Added the 'etag' property to the schema.
 	 *
 	 * @todo Cache the return value?
 	 *
@@ -210,7 +210,7 @@ public static function get_json_schema(): array {
 					'required'    => true,
 					'readonly'    => true, // Omit from REST API.
 				),
-				'eTag'      => array(
+				'etag'      => array(
 					'description' => __( 'The ETag for the URL Metric.', 'optimization-detective' ),
 					'type'        => 'string',
 					'required'    => false, // To be made required in a future release.
@@ -434,7 +434,7 @@ public function get_uuid(): string {
 	 */
 	public function get_etag(): ?string {
 		// Since the ETag is optional for now, return null for old URL Metrics that do not have one.
-		return $this->data['eTag'] ?? null;
+		return $this->data['etag'] ?? null;
 	}
 
 	/**
diff --git a/plugins/optimization-detective/storage/rest-api.php b/plugins/optimization-detective/storage/rest-api.php
index 51d004ea0..9b3b962ca 100644
--- a/plugins/optimization-detective/storage/rest-api.php
+++ b/plugins/optimization-detective/storage/rest-api.php
@@ -188,7 +188,7 @@ function od_handle_rest_request( WP_REST_Request $request ) {
 					// Now supply the readonly args which were omitted from the REST API params due to being `readonly`.
 					'timestamp' => microtime( true ),
 					'uuid'      => wp_generate_uuid4(),
-					'eTag'      => $request->get_param( 'eTag' ),
+					'etag'      => $request->get_param( 'eTag' ),
 				)
 			)
 		);