Q: my iMessage keeps getting error when activated

If you get an error when trying to activate iMessage or FaceTime - Apple Support

Log out of Find iPhone

Sign out of iCloud

Reboot your phone -

Restart your iPhone, iPad, or iPod touch - Apple Support

Sign back in

See if that helps

Constant iOS Apple ID Password Verification Pop-Up Alert Fix

Resolving the continuous Apple ID password verification request is usually by doing the following:

1. When you see the Apple ID Verification pop-up message, choose “Settings”
2. Sign into the Apple ID with the password for the account as usual, this will make the message go away temporarily
3. Next, back up the iPhone, iPad, or iPod touch to iCloud and iTunes, you need to backup the device because you likely need to update iOS software
4. Open the Settings app and go to “General” followed by “Software Update”, install any software updates that are waiting available – If you’re already on the latest version of iOS and there are no software updates available skip this step, reboot the device, and go to the next
5. When the device boots back up, go back to “Settings”, then to “iCloud” and tap on the Apple ID username and email address, then sign in to iCloud when requested
6. Exit out of Settings, you shouldn’t see the Apple ID verification pop-up again

A bit of jumping around, a possible iOS update, a reboot, and multiple logins for the same Apple ID and iCloud account, but for most users this resolves the issue. Contrary to some other reports on discussion boards, you do not need to log out or change the Apple ID to resolve the issue, simply verifying the password and rebooting is usually enough.

If you reboot the device after this, you should no longer see the lock-screen error message requesting Apple ID password verification.