Your account has been disabled in the App Store and iTunes.
Attempting to download or purchase items in the iOS App Store suddenly began returning:
Your account has been disabled in the App Store and iTunes.
Testing in iTunes under macOS returned the same message, though with a thoughtful addendum:
Your account has been disabled in the App Store and iTunes. For assistance, contact iTunes Support.
Logging in via iCloud.com still worked, so next tried changing payment info via https://appleid.apple.com/account/manage > Payment & Shipping > Edit, sadly to no avail:
Payment information could not be updated. This Apple ID has been disabled, and cannot redeem codes.
Called 1-800-MY-IPHONE. Transferred to "iTunes Support" (for which a direct number was not available, I was told (later discovered that https://getsupport.apple.com offers email, phone callback, and chat support for iTunes)). Instructed to click "Generate PIN" at the bottom of the https://applied.apple.com page and share it with the customer service rep, who kindly resolved the issue (which she said had been caused by the credit card having been replaced following a fraud alert).
/mac | Jan 02, 2019