The problem resides with old Apple devices set up with the old iTunes/iCloud email account that doesn't automatically update to the new AppleID when changed. For example, we have one iPad setup with firstname.lastname@example.org which has been transitioned to email@example.com. This worked honky-dory until updates became an issue as of tonight.
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Try All Possible Passwords for iTunes Account. The first method which you should try if you are …
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How to Change iTunes Account on iPhone or iPad
How to Change Apple ID Email, Billing Address, Credit Card Feb 20, 2020 How to Change iTunes Account on iPhone or iPad Jan 16, 2018 How Do I Change My Apple ID On My iPhone? The Fix!