sounds like what happened on my iphone yesterday, with the new ios beta; i finally got it working by turning on messages on icloud; try that. i dealt with this for 5 hours last night, even with apple help. but icloud on (on both my mac & iphone) fixes it (and, sigh, bumps up my icloud storage)...
I have it turned on on the phone? i even disabled it? and re enabled it? the problem in on my MAC!!! **** wont let me log into my account and when it does it says Imessages are inactive?
right, and on your mac, in messages>preferences>accounts, is icloud enabled or disabled? once i enabled that (on both devices), my messages are working again (on both devices).
is 'messages' enabled in the icloud setting on your phone? and on your mac? again, these things got my texts working; before that, i had the same issue you're having. try what i've suggested...
ur no help, its more serious than that
here, this will entertain you: i JUST updated my mac to 10.13.4 Beta (17E150g), and now, i can't sign in to message on my mac ("an error occured during authentication)... and an "imagent quit unexpectedly" window pops up every minute...
if i figure a way out of it, will post again.
anyone else???
EDIT: 6th try, and am signed into messages on my mac (and, unlike the previous beta, the icloud option is now greyed out). seriously, apple needs to figure this out.
EDIT EDIT: working after 3rd reboot; prob just needed time to sync? and icloud is still greyed out. but it's working...