I am currently facing the same problem, enabled Live Text and couldn't get selected text so had to use VNRecognizeTextRequest instead. Have you found a solution to this?

If you have a website for the app, you could copy the referral link to the user's clipboard when they visit it and when the user downloads the app, you can check their clipboard for the link. This is the same way firebase does these deep links.

I replied to app review saying that the problem may just be on their side and they tested the IAPs with a different Apple ID. It worked and my app got approved so I think that the problem was on their side since I didn't change anything.