Apple Mac App Store: "Unable to download item. Please try again later": The problem may be that you are not the purchaser.

I was logged into my admin account on my daughter's Big Sur Air and saw the usual nag to update Apps. When I tried though I got  "Unable to download item. Please try again later."

It never works to try again later. This is a typically useless Apple error message produced when something has gone wrong with their complex FairPlay DRM authentication. There are a range of fixes that Google shows but, even after I figured out the bug (a design fail of this sort is a bug) I couldn't find anything that explained the fix [1]. So here you go!

The problem happens on a multi-user Mac with multiple admins installing software using different Apple Store Apple IDs. It might also require that automatic updates are not enabled and it might require that Family Sharing is enabled.

Every admin gets notification of a pending update, but only the FairPlay determined DRM owner can actually successfully do the update. Other admins who try get the useless error message.

The fix on Big Sur's Mac App Store is to cast your gaze down to the bottom left corner of the App Store window. There you see a user name. Click on the user name and you'll see an "Account" screen. At the top of the "Account" screen is a "Purchased by" drop down with the user name of every family sharing member [1]. Switch between Accounts here to find who has the "update" for the problem app. Then update. Continue until all apps are updated.

It will be interesting to see if this is handled better in Monterey. I can imagine several potential fixes!

[1] As every Old will repeat ad nauseam, the Google web was much better 20 years ago.