iOS: In-App-Purchase fails for some users in production -

I recently released an iPad app in which there is a non-consumable "pro upgrade" - in-app purchase The style of

It works for most users, and it works while testing, however, I get daily reports of IAP waste for some AAP customers.

This is the worst kind of bug:

• For most people, it seems to work properly
• For some people, It works after rebooting the device or logging in from the app store.
• For some others, nothing seems and they can not buy.

And I do not have any remote logging applied ...

This is for all people who can not make purchases, usually an error That comes, which says that their Apple ID password is incorrect, after confirming the purchase.

The app purchasing button only appears when the IAP product was successfully received from the Apple server.

I'm not sure how it's going on I was initially thinking that it is on the side of the apple, but it tells the number of people reporting it to be something with my app.

How is this the best practice to debug? Thanks!