~I did it and have a fix! It’s extremely simple; My iPhone would NOT sync iMessage intuitively with my Mac. It’s now working perfectly. _ALL YOU HAVE TO DO_
Go to https://appleid.apple.com and make sure under phone numbers (Column on left side) you have your cell phone number filled out for all of the columns! Nothing will change other than the fact that iMessage will sync all messages from iPhone, under regular apple ID.
After you do that ^ CLOSE iMessage on your Mac, then reopen.
Let me know if this works for you, or if you need more assistance - firstname.lastname@example.org
Best of luck,