I'm having the same issue since about mid Sept now - I've tried everything except 'wiping' the phone - I refuse to do that since Everything else is working! Using Messages+, recently tried Google Messenger, doesn't work on that either .
I cannot send Photos, Gifs or Group texts..... using Moto Z Play... Android 8.0.0... so frustrating! Pretty sure some update wither changed some setting or something.
MusicFan1, we certainly want to get this resolved. Have we had the opportunity to access your account and troubleshoot with you?