Apple ID Switch

When I got my son his phone 2 years ago, I used my Apple ID, recently he got his own Apple ID and after a few days when he tried to update an app on his phone it asked him to enter the Apple ID password for the old account, but didn’t accept it. We’ve tried changing the password, putting in the password for both accounts, but no matter what we are unable to update any existing apps even with family sharing enabled.

and because I know this is often the suggestion apple makes, for 2 years we didn’t know better and shared an Apple ID but recently got him his own, but are having issues in the App Store regarding existing apps