I have tested it on my iPhone. It was working smoothly the whole way through. I found that I could get the indefinite load on the app button if I go into airplane mode at just the right time.
That being said, through normal use, there were no issues – the “buy now” button load animation would play until the purchase was confirmed, then everything continued as planned.
After updating to the newest iOS (14.7.1), I found that the payment confirmation takes longer than before, but it still goes through OK.
Hmm - ok - I haven’t implemented IAP in my app (yet) in Adalo. I’ve done it in an app I built using flutter last year and it was accepted so I’m hoping it will be ok in Adalo. Sorry I can’t offer any other advice. You could perhaps try submitting again and it may have been a momentary lapse in performance at the time they tested it?