Apple - iTunes Store Sign in Failure: "%%appleId%%"

I had this happen to me and what worked was intentionally failing the Touch ID (or face I think it doesnt matter) so it gives you the option to type in your apple id password

I went to System Preferences > Face ID and Passcode (which required me to enter my device password) and turned off Face ID for the App Store.

Once I did that, I attempted to make an in app purchase and was again sent to verify my info, but this time was able to do this successfully after inputting my CVV.

I then turned FaceID back on for the AppStore.

This happened to me as well a few days ago. I fixed it by turning off the passcode to unlock the iPad (which required me to enter the apple id password) and turning off Face Time for App Store purchases. Then I turned passcode back on (which again required my apple id password). Then when I went to do an in-app purchase it failed, required verification, but this time it actually asked for a password rather than giving the "%%appleId%%" error. The in-app purchased completed. I then turned face time back on for App Store purchases and now face time works just great for in-app purchases, no errors or failed verifications anymore.

As a developer, this has got to be happening to more folks than just us. You'd think Apple would have maetris that would be showing a general drop in in app purchases, but not a corresponding drop to app purchases and they would track the problem down and fix it.

There are also anecdotal reports that you might have to fail your fingerprint / Face ID or disable / re-enable more than once to clear this error condition. On most, the first fix works, though.