App Approved but IAP's Waiting for review, not getting reviewed
I noticed from experience, that even when your app is approved, the IAP can take quite a while to get approved, especially when you have translated the IAP in (many) other languages, it seems that those needs to go to different teams that can understand the translation, to see if you deliver on your promise.

So in that mean time users get "Product not available" in the App. In my latest app I have 2 IAPs, the 2st one is approved 2 days after the App approval, the second which has more languages, is not yet approved (3rd day now).