If you got "Unauthorized" error in the Cloud Panel and you have already disabled 2-factor authentication, then try to change the iCloud Password.
To update iCloud Password, follow steps below:
1. Login to https://appleid.apple.com and change the Password.
2. Enter the new password in the Cloud panel - Device - Device Management and click "Update Password".
3. Check on the iPhone/iPad to see if it pops up a password change dialogue and update the password on the device.