This page gives you some hints when you get an error or run into a problem for communication scenario SAP_COM_0523 or SAP_COM_0527.

When saving the communication arrangement a synchronous call to the ALM platform is executed. If no LMS ID is retrieved the registration was not successful. There might be several reasons:

1. Cannot create HTTP Client: Error when setting oauth token
   The field Token Endpoint in the communication system is not correct. It must be the SAP Cloud ALM service key parameter "url" + /oauth/token