When running the Client-side APEX Plug-in, turn APEX Debug on and check the debug logs.

When using the Server-side PL/SQL API, ame_api_pkg, you can enable debug by calling:

 ame_api_pkg.g_debug := 'Local';

AME will now provide the JSON that is being send to the AME server in a global variable g_debug_json. Check this JSON or send this JSON to to get help for your specific case.