Need to restore in-app purchase from iTunes backup

I made in-app purchases in an app that is no longer available in the iTunes Store. Fortunately, everything was backed up via iTunes in an old iPhone 5 backup.

I can and have of course installed the app file to my current phone, but since the app isn’t in the store anymore, trying to restore those past in-app purchases that essentially make it fully functional is a no-go.

Can I extract them from the backup?