Hi Stevetx2,
Thanks for posting in Apple Support Communities.
We understand Messages are not working on your Mac. If your Mac is running the latest software with the most recent update fixes, make sure you have a stable Wi-Fi network and using Messages with an active Apple ID. Provide any specific error messages you receive, excluding any personal information.
To address the behavior with messages not working perform the steps found in If you can’t send or receive messages on your Mac - Apple Support.
Try these steps first
After trying each step below, try to send a message again.
* Restart your Mac. Choose Apple menu > Restart, then click Restart.
* Make sure that your software is up to date. Learn how to update the software on your Mac.
* Make sure that your Mac is connected to the Internet. To check your Internet connection, try loading a page in Safari or another web browser.
* Check that the date and time is set correctly on your Mac.
* Make sure that you enter the correct phone number or email address for the contact.
If you see ‘This user is not registered with iMessage’
If you try to send a message and see an alert that the person isn’t registered with iMessage, the message is trying to send using SMS/MMS. Make sure Text Message Forwarding is set up and your iPhone is powered on.
If your contacts see your email instead of your phone number
If you can send messages but your contacts see your email address instead of your phone number, make sure that you're signed in to iMessage with the same Apple ID on all your devices. Learn how to add your phone number to Messages on your Mac.
Regards.
