If you can’t send or receive messages using Messages on Mac
If you can’t send or receive messages using the Messages app on Mac, try these solutions.
Check our System Status page to find out whether iMessage is experiencing a service outage.
Make sure that your Mac is connected to the Internet. You should be able to load webpages and receive email, for example.
Restart your Mac.
Check Date & Time settings to make sure that the date and time are correct. Can't change the time or time zone?
Make sure that you're addressing the message to the correct phone number or email address.
If Messages shows an alert stating that the person is not registered with iMessage, or you can't continue SMS/MMS conversations that you send and receive on your iPhone, make sure that your iPhone is turned on and you have set up Text Message Forwarding correctly.
Learn what to do if your Mac says that it couldn't sign in to iMessage, or that it couldn't contact the iMessage server.
If you still can’t send or receive messages, contact Apple Support.