There is additional information provided on the Twilio side when a Registration has problems. Could the error code be presented in the GHL Trust Center in addiiton to the word REJECTED ? That would be a great help to resolve the issue with an application. https://support.twilio.com/hc/en-us/articles/15778026827291-Why-Was-My-A2P-10DLC-Campaign-Registration-Rejected-
For example, error 30893 would be a link to https://www.twilio.com/docs/api/errors/30893