The A2P use case you are trying to specify in the request is not a valid use case.
The A2P use case specified in the request is not a valid A2P use case.
Verify that you are spelling the use case correctly in your request and that it is using all uppercase letters. The following resource can also be used to retrieve all valid A2P use cases for a specific Messaging Service: https://messaging.twilio.com/v1/Services/MGXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Compliance/Usa2p/Usecases