Q: This computer is no longer authorized for purchased items that are on this iPad

You might try this article:

iTunes repeatedly prompts to authorize computer to play iTunes Store purchases - Apple Support

Carefully think about the Apple ID and password that were used to purchase items from the iTunes Store that are currently on the iPad.

There may be more than one such Apple ID.

I'm having the same problem.  My husband and I share this iPad and we have set up family sharing.  Husband thinks that at some point we each synced the iPad to our respective Macs.  We have also each purchased apps using our separate iTunes accounts before I set up the family sharing.  How can we fix this error message?  I bought an new app recently and now can't get it onto the iPad.  Grateful for any wisdom you can share!  Thanks!

Easy fix. You need to make sure that you have authorized that computer to be used with every APPLE ID that will be syncing to it.

For example, my Mac Air syncs my iPhone with my Apple ID. In order to sync my daughter's iPhone (who is on my Family Share) I had to sign into iTunes on my Mac Air with HER Apple ID and authorize the computer. Now that both Apple ID's have authorized this computer, they can sync music, apps etc.

Hope that fixes it!

-J