diff --git a/libs/Microsoft.MixedReality.WebRTC.Native/include/api.h b/libs/Microsoft.MixedReality.WebRTC.Native/include/api.h
index 80c52a488..992a0f5c8 100644
--- a/libs/Microsoft.MixedReality.WebRTC.Native/include/api.h
+++ b/libs/Microsoft.MixedReality.WebRTC.Native/include/api.h
@@ -24,6 +24,22 @@ rtc::Thread* UnsafeGetWorkerThread();
 
 extern "C" {
 
+//
+// Errors
+//
+
+using mrsResult = std::uint32_t;
+
+constexpr const mrsResult MRS_SUCCESS{0};
+
+// Peer conection (0x0xx)
+constexpr const mrsResult MRS_E_INVALID_PEER_HANDLE{0x8000001};
+constexpr const mrsResult MRS_E_PEER_NOT_INITIALIZED{0x8000002};
+
+// Data (0x3xx)
+constexpr const mrsResult MRS_E_SCTP_NOT_NEGOTIATED{0x8000301};
+constexpr const mrsResult MRS_E_INVALID_DATA_CHANNEL_ID{0x8000302};
+
 //
 // Generic utilities
 //
@@ -243,7 +259,7 @@ mrsPeerConnectionAddLocalAudioTrack(PeerConnectionHandle peerHandle) noexcept;
 /// - If id >= 0, then it adds a new out-of-band negotiated channel with the
 /// given ID, and it is the responsibility of the app to create a channel with
 /// the same ID on the remote peer to be able to use the channel.
-MRS_API bool MRS_CALL mrsPeerConnectionAddDataChannel(
+MRS_API mrsResult MRS_CALL mrsPeerConnectionAddDataChannel(
     PeerConnectionHandle peerHandle,
     int id,             // -1 for auto, >=0 for negotiated
     const char* label,  // optional, can be null or empty string
diff --git a/libs/Microsoft.MixedReality.WebRTC.Native/src/api.cpp b/libs/Microsoft.MixedReality.WebRTC.Native/src/api.cpp
index 280eaf2b8..d7431fb04 100644
--- a/libs/Microsoft.MixedReality.WebRTC.Native/src/api.cpp
+++ b/libs/Microsoft.MixedReality.WebRTC.Native/src/api.cpp
@@ -498,7 +498,7 @@ mrsPeerConnectionAddLocalAudioTrack(PeerConnectionHandle peerHandle) noexcept {
   return false;
 }
 
-bool MRS_CALL mrsPeerConnectionAddDataChannel(
+mrsResult MRS_CALL mrsPeerConnectionAddDataChannel(
     PeerConnectionHandle peerHandle,
     int id,
     const char* label,
@@ -519,7 +519,7 @@ bool MRS_CALL mrsPeerConnectionAddDataChannel(
         DataChannelBufferingCallback{buffering_callback, buffering_user_data},
         DataChannelStateCallback{state_callback, state_user_data});
   }
-  return false;
+  return MRS_E_INVALID_PEER_HANDLE;
 }
 
 void MRS_CALL mrsPeerConnectionRemoveLocalVideoTrack(
diff --git a/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.cpp b/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.cpp
index 8f80db190..87db0ebb3 100644
--- a/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.cpp
+++ b/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.cpp
@@ -160,12 +160,12 @@ bool PeerConnection::AddDataChannel(
     config.id = id;
   } else {
     // Valid IDs are 0-65535 (16 bits)
-    return false;
+    return MRS_E_INVALID_DATA_CHANNEL_ID;
   }
   if (!sctp_negotiated_) {
     // Don't try to create a data channel without SCTP negotiation, it will get
     // stuck in the kConnecting state forever.
-    return false;
+    return MRS_E_SCTP_NOT_NEGOTIATED;
   }
   std::string labelString;
   if (label)
@@ -275,8 +275,8 @@ bool PeerConnection::CreateOffer() noexcept {
     options.offer_to_receive_audio = true;
     options.offer_to_receive_video = true;
   }
-  if (!data_channel_from_id_.empty()) {
-    sctp_negotiated_ = true;
+  if (data_channel_from_id_.empty()) {
+    sctp_negotiated_ = false;
   }
   peer_->CreateOffer(this, options);
   return true;
@@ -299,6 +299,9 @@ bool PeerConnection::SetRemoteDescription(const char* type,
                                           const char* sdp) noexcept {
   if (!peer_)
     return false;
+  if (data_channel_from_id_.empty()) {
+    sctp_negotiated_ = false;
+  }
   std::string sdp_type_str(type);
   auto sdp_type = webrtc::SdpTypeFromString(sdp_type_str);
   if (!sdp_type.has_value())
diff --git a/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.h b/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.h
index 2f0012c6a..33c46ce73 100644
--- a/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.h
+++ b/libs/Microsoft.MixedReality.WebRTC.Native/src/peer_connection.h
@@ -232,7 +232,7 @@ class PeerConnection : public webrtc::PeerConnectionObserver,
   /// data channel is created before the connection is established, which will
   /// force the connection to negotiate the necessary SCTP information. See
   /// https://stackoverflow.com/questions/43788872/how-are-data-channels-negotiated-between-two-peers-with-webrtc
-  bool sctp_negotiated_ = false;
+  bool sctp_negotiated_ = true;
 
  private:
   PeerConnection(const PeerConnection&) = delete;
diff --git a/libs/Microsoft.MixedReality.WebRTC/PeerConnection.cs b/libs/Microsoft.MixedReality.WebRTC/PeerConnection.cs
index e1174fc06..612983031 100644
--- a/libs/Microsoft.MixedReality.WebRTC/PeerConnection.cs
+++ b/libs/Microsoft.MixedReality.WebRTC/PeerConnection.cs
@@ -672,9 +672,8 @@ public void Dispose()
         /// On UWP this requires the "webcam" capability.
         /// See <see href="https://docs.microsoft.com/en-us/windows/uwp/packaging/app-capability-declarations"/>
         /// for more details.
-        /// 
-        /// This method throws an exception if the peer connection is not initialized.
         /// </remarks>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public Task AddLocalVideoTrackAsync(VideoCaptureDevice device = default(VideoCaptureDevice), bool enableMrc = false)
         {
             ThrowIfConnectionNotOpen();
@@ -692,7 +691,7 @@ public void Dispose()
         /// <summary>
         /// Remove from the current connection the local video track added with <see cref="AddLocalAudioTrackAsync"/>.
         /// </summary>
-        /// <remarks>This method throws an exception if the peer connection is not initialized.</remarks>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public void RemoveLocalVideoTrack()
         {
             ThrowIfConnectionNotOpen();
@@ -707,9 +706,8 @@ public void RemoveLocalVideoTrack()
         /// On UWP this requires the "microphone" capability.
         /// See <see href="https://docs.microsoft.com/en-us/windows/uwp/packaging/app-capability-declarations"/>
         /// for more details.
-        /// 
-        /// This method throws an exception if the peer connection is not initialized.
         /// </remarks>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public Task AddLocalAudioTrackAsync()
         {
             ThrowIfConnectionNotOpen();
@@ -727,7 +725,7 @@ public Task AddLocalAudioTrackAsync()
         /// <summary>
         /// Remove from the current connection the local audio track added with <see cref="AddLocalAudioTrackAsync"/>.
         /// </summary>
-        /// <remarks>This method throws an exception if the peer connection is not initialized.</remarks>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public void RemoveLocalAudioTrack()
         {
             ThrowIfConnectionNotOpen();
@@ -756,6 +754,9 @@ public void RemoveLocalAudioTrack()
         /// <param name="reliable">Indicates whether data channel messages are reliably delivered
         /// (see <see cref="DataChannel.Reliable"/>).</param>
         /// <returns>Returns a task which completes once the data channel is created.</returns>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
+        /// <exception cref="InvalidOperationException">SCTP not negotiated.</exception>
+        /// <exception cref="ArgumentOutOfRangeException">Invalid data channel ID, must be in [0:65535].</exception>
         public async Task<DataChannel> AddDataChannelAsync(ushort id, string label, bool ordered, bool reliable)
         {
             if (id < 0)
@@ -783,6 +784,9 @@ public async Task<DataChannel> AddDataChannelAsync(ushort id, string label, bool
         /// <param name="reliable">Indicates whether data channel messages are reliably delivered
         /// (see <see cref="DataChannel.Reliable"/>).</param>
         /// <returns>Returns a task which completes once the data channel is created.</returns>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
+        /// <exception cref="InvalidOperationException">SCTP not negotiated.</exception>
+        /// <exception cref="ArgumentOutOfRangeException">Invalid data channel ID, must be in [0:65535].</exception>
         public async Task<DataChannel> AddDataChannelAsync(string label, bool ordered, bool reliable)
         {
             return await AddDataChannelAsyncImpl(-1, label, ordered, reliable);
@@ -798,6 +802,9 @@ public async Task<DataChannel> AddDataChannelAsync(string label, bool ordered, b
         /// <param name="reliable">Indicates whether data channel messages are reliably delivered
         /// (see <see cref="DataChannel.Reliable"/>).</param>
         /// <returns>Returns a task which completes once the data channel is created.</returns>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
+        /// <exception cref="InvalidOperationException">SCTP not negotiated.</exception>
+        /// <exception cref="ArgumentOutOfRangeException">Invalid data channel ID, must be in [0:65535].</exception>
         private async Task<DataChannel> AddDataChannelAsyncImpl(int id, string label, bool ordered, bool reliable)
         {
             // Preconditions
@@ -821,13 +828,22 @@ private async Task<DataChannel> AddDataChannelAsyncImpl(int id, string label, bo
             // Create the native channel
             return await Task.Run(() =>
             {
-                if (NativeMethods.PeerConnectionAddDataChannel(_nativePeerhandle, id, label, ordered, reliable,
-                args.MessageCallback, userData, args.BufferingCallback, userData, args.StateCallback, userData))
+                uint res = NativeMethods.PeerConnectionAddDataChannel(_nativePeerhandle, id, label, ordered, reliable,
+                args.MessageCallback, userData, args.BufferingCallback, userData, args.StateCallback, userData);
+                if (res == 0)
                 {
                     return dataChannel;
                 }
                 handle.Free();
-                return null;
+                if (res == 0x80000301) // MRS_E_SCTP_NOT_NEGOTIATED
+                {
+                    throw new InvalidOperationException("Cannot add a first data channel after the connection handshake started. Call AddDataChannelAsync() before calling CreateOffer().");
+                }
+                if (res == 0x80000302) // MRS_E_INVALID_DATA_CHANNEL_ID
+                {
+                    throw new ArgumentOutOfRangeException("id", id, "Invalid ID passed to AddDataChannelAsync().");
+                }
+                throw new Exception("AddDataChannelAsync() failed.");
             });
         }
 
@@ -854,24 +870,44 @@ internal void SendDataChannelMessage(int id, byte[] message)
         /// <param name="sdpMid"></param>
         /// <param name="sdpMlineindex"></param>
         /// <param name="candidate"></param>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public void AddIceCandidate(string sdpMid, int sdpMlineindex, string candidate)
         {
             ThrowIfConnectionNotOpen();
             NativeMethods.PeerConnectionAddIceCandidate(_nativePeerhandle, sdpMid, sdpMlineindex, candidate);
         }
 
+        /// <summary>
+        /// Create an SDP offer message as an attempt to establish a connection.
+        /// </summary>
+        /// <returns><c>true</c> if the offer was created successfully.</returns>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public bool CreateOffer()
         {
             ThrowIfConnectionNotOpen();
             return NativeMethods.PeerConnectionCreateOffer(_nativePeerhandle);
         }
 
+        /// <summary>
+        /// Create an SDP answer message to a previously-received offer, to accept a connection.
+        /// </summary>
+        /// <returns><c>true</c> if the offer was created successfully.</returns>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public bool CreateAnswer()
         {
             ThrowIfConnectionNotOpen();
             return NativeMethods.PeerConnectionCreateAnswer(_nativePeerhandle);
         }
 
+        /// <summary>
+        /// Pass the given SDP description received from the remote peer via signaling to the
+        /// underlying WebRTC implementation, which will parse and use it.
+        /// 
+        /// This must be called by the signaler when receiving a message.
+        /// </summary>
+        /// <param name="type">The type of SDP message ("offer", "answer", "ice")</param>
+        /// <param name="sdp">The content of the SDP message</param>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         public void SetRemoteDescription(string type, string sdp)
         {
             ThrowIfConnectionNotOpen();
@@ -885,6 +921,7 @@ public void SetRemoteDescription(string type, string sdp)
         /// Utility to throw an exception if a method is called before the underlying
         /// native peer connection has been initialized.
         /// </summary>
+        /// <exception cref="InvalidOperationException">The peer connection is not intialized.</exception>
         private void ThrowIfConnectionNotOpen()
         {
             lock (_openCloseLock)
@@ -1044,7 +1081,7 @@ public static extern void PeerConnectionRegisterARGBRemoteVideoFrameCallback(Int
 
             [DllImport(dllPath, CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi,
                 EntryPoint = "mrsPeerConnectionAddDataChannel")]
-            public static extern bool PeerConnectionAddDataChannel(IntPtr peerHandle, int id, string label,
+            public static extern uint PeerConnectionAddDataChannel(IntPtr peerHandle, int id, string label,
                 bool ordered, bool reliable, PeerConnectionDataChannelMessageCallback messageCallback,
                 IntPtr messageUserData, PeerConnectionDataChannelBufferingCallback bufferingCallback,
                 IntPtr bufferingUserData, PeerConnectionDataChannelStateCallback stateCallback,