Here's how to solve pesky iMessage and FaceTime activation problems - TechnW3

Getting an authentication error trying to log into iMessage or FaceTime? Try this fix!

Apple rightfully has a reputation for having its products "just work." And 99% of the time, that adage holds. Until it doesn't. When things do go wrong, Apple's error messages can be cryptic, at times offering no obvious clue as to how to remedy them. One such error is the "Authentication Error" message when trying to log into iMessage and FaceTime on your Mac, even if you've successfully logged into iCloud.

We know just how frustrating it can be when your best Mac isn't letting you use basic functions of the computer; the good news is there a fix for Message and FaceTime activation issues on macOS Big Sur.

The problem

For a non-obvious reason, my previously properly running Mac could no longer log into iMessage or FaceTime despite successfully logging into iCloud. Notes synced, Documents synced, Photos were working, etc.

Trying to log into iMessage triggers my two-factor authentication mechanism as expected. But when prompted for my iCloud username and password, and after a long timeout period, I get an "Authentication Error."

The potential fix

The fix involves getting Apple's servers to re-initialize your Mac hardware to be allowed to access your iCloud services.

Log out of iCloud on your Mac

Open System Preferences.
Click Apple ID.
Click Overview.
Click Sign Out…
Follow the instructions to keep or delete iCloud data like calendars, reminders, and photos from your Mac.
Restart your Mac.