I migrated MLAPI to NetCode.
Stand alone version is ok. but, WebGL build occurred runtime error.
WebGL build version can’t connect to local host.
The runtime error is KeyNotFoundException.

I checked error reason.
ILPPMessageProvider is empty __network_message_types list.
In WebGL build, post processing code generator not applied.
(editor/codegen script. ILPostProcessor.)
Test infomation.
Unity version: 2020.3.17f1
NetCode : 1.0.0-pre.6
Apply commit:
fix: Make the adapter compile on WebGL
(fix: Make the adapter compile on WebGL by simon-lemay-unity · Pull Request #1802 · Unity-Technologies/com.unity.netcode.gameobjects · GitHub)
Test Code : NetCode Test project. ConnectionApproval
(com.unity.netcode.gameobjects/testproject at develop · Unity-Technologies/com.unity.netcode.gameobjects · GitHub)
Transport : WebSocket Transport
(multiplayer-community-contributions/Transports at main · Unity-Technologies/multiplayer-community-contributions · GitHub)
Other problem: NetCode UnetTransport websocket not contain service name.