iPhone 16 Pro Max Messages not syncing with macOS Sequoia

I have a mac mini running sequoia, iphone 16 pro max ios 18.5 and can't get messages to send from mac that will send from phone. Before I replaced phone recently - no problem at all. I have looked up how to fix and nothing has worked. This is becoming a real time suck. Help?

[Re-Titled by Moderator]

Original Title: Messages - ahhhhhhhhhh