iOS App Update hangs without an error message in infinite download: a general approach

Apple's FairPlay DRM management is notoriously fragile. It can be confused by family sharing, Screen Time controls, payment method changes, and, heaven forfend, mixed Apple IDs on a device.

Once Apple's DRM gets confused there's often no user accessible error message (PS. This is a bug [1]). The app just hangs. So when I realized my (manual) App Store updates were not completing I was not completely surprised. Recently I had:

1. Changed payment methods. I made my Apple Card's award balance (1-2% transaction) the default payment method (so it always gets emptied)
2. Enabled Screen Time account change restrictions to mitigate the harm of Apple's biggest current security issue.

I fixed the problem in the usual way (see Apple's article on this as well):

1. [Switch to manual update if you've been using automatic]
2. Verify Apple ID payment methods look correct
3. Turn off Screen Time [Apple doesn't mention this.]
4. Restart phone (power off/on)
5. Download a new free app from App Store [An old method, still useful]
6. Verify I can now update one of the pending apps.
7. Update All
8. Turn Screen Time back on.
9. [Turn auto update back on if you like that.]

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[1] Failure to generate a user notification of a failed interaction is, of course, a bug. Regardless of whether there's a bug in the interaction processing (which there is, so that's another one).