How to set up iMessage on your MacSource: Joseph Keller / iMore

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

  1. Open System Preferences.
  2. Click Apple ID.

    How to log out of iCloud on macOS: Open system preferences and then click Apple ID. Source: iMore

  3. Click Overview.
  4. Click Sign Out…

    How to log out of iCloud on macOS: Click Overview and then click Sign OutSource: iMore

  5. Follow the instructions to keep or delete iCloud data like calendars, reminders, and photos from your Mac.

    How to log out of iCloud on macOS:Source: iMore

  6. Restart your Mac.

Log into your iCloud.com web account

  1. Navigate to iCloud.com in Safari.
  2. Log in with your iCloud credentials.

    How to Log into iCloud.com: Navigate to icloud.com and then log in to your cloud accountSource: iMore

  3. Click Account Settings.
  4. Click your problematic Mac under My Devices.

    How to Log into iCloud.com: Click account settings and then click on the Mac that is having issues.Source: iMore

  5. Click the X next to the Mac.
  6. Click Remove.

    How to Log into iCloud.com: Click the Source: iMore

  7. Click Done.

    How to Log into iCloud.com: ClickSource: iMore

Sign back into iCloud on your Mac

  1. Open System Preferences.
  2. Click Sign In.

    Sign in to iCloud on Mac: Open System Preferences, and then click Sign InSource: iMore

  3. Sign in with your iCloud credentials.
  4. Enter your Mac sign-in credentials.

    Sign in to iCloud on Mac:  Sign in with your iCloud credentials and then enter your Mac sign in credentials.Source: iMore

  5. Click OK.

    Sign in to iCloud on Mac: Click OKSource: iMore

Once you're signed back into iCloud on your Mac, you should automatically be signed back into Messages and FaceTime.

Final comments

This is but one solution (of the myriad of suggestions found online) that worked for me. Let us know in the comments if this fix helped you too!

macOS Big Sur

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