How to fix iMessage not working on iPhone 16 Pro Max?

imessage stopped working a few days ago. I turned FaceTime and iMessage off and back on, restarted the phone, rebooted, still nothing. Call tech support with Verizon, they said it could be that my phone was outdated, had a 12pro max, got a new phone 16 pro max, and I’m still having the same problem. I’ve deleted messages, changed all of the phone in contacts to iPhone (instead of mobile or phone) and still nothing. I can only send text messages when it does go through. I’ve turned RCS and MMS message off and on, with no resolve. The software is 18.4.1. Any advice?

[Re-Titled by Moderator]