In order to sort this out I'd need details about what you did to merge the accounts (which officially isn't supported and not 100% possible an Apple's directions are What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support). It may be if you signed out of one ID on a device and signed into another on the same device that relic items may have persisted from the old ID unless you erased the device first. That's one step in "merging" accounts but it can lead to this kind of mess. The trouble is digging them out. If it's apps, rather than setting them to update automatically, change the settings to manually update them. Then when you've got a batch go through them one by one until you see one that gripes about needing a different password. There's a bit more along these lines in this section from: If you can't connect or sign in to iCloud - Apple Support
If you are repeatedly prompted to enter your Apple ID password on your Mac or iOS device
- If you have recently restored your iPhone, iPad or iPod touch from an iCloud backup, the restore may not have completed. Stay connected to a reliable Wi-Fi network and power source until the restore finishes. Follow these steps if iCloud Backup couldn't be completed or you can't restore ( If you can't back up to iCloud - Apple Support ).
- If you recently changed your Apple ID password, you might need to update your sign-in information ( What to do after you change your Apple ID or password - Apple Support ) with iCloud services you use. Make sure that each service is using your updated sign-in information on your device.
- Check if you have Automatic Downloads enabled ( How to manually update apps on your Apple device - Apple Support ). If there is content ready to be downloaded, you may be prompted to enter your Apple ID and password to continue. Learn how to resume interrupted downloads (If there's an issue when you redownload apps, movies, or other content from Apple - Apple Support ).
- If you are an organizer, parent, or guardian of a Family Sharing group, check if the prompt is a request from a child family member to make an iTunes Store purchase. You can then approve or decline the request ( Approve what kids buy with Ask to Buy - Apple Support ).
Accounts don't necessarily disappear if you stop using them. Here's some legalese:
Legal - iCloud - Apple
VII. B "In addition, Apple may terminate your Account upon 30 days’ prior notice via email to the address associated with your Account if (a) your Account has been inactive for one (1) year; or (b) there is a general discontinuance of the Service or any part thereof."
Legal - iCloud - Apple
II. M. "If a device has not backed up to iCloud for a period of one hundred and eighty (180) days, Apple reserves the right to delete any backups associated with that device."
About "invalid" and "not supported" accounts, the recommendations I have seen are to contact Apple about the account:
Contact Apple. Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support
