I have been charged again today for the upgrade i did in 2019!

Yesterday without notice my iPad Midi Guitar 2 stopped working. I deleted the app and reinstalled. I was asked again to repurchase the $ 9.99 upgrade which I had already bought in 2019 , with a notice explaining I would not be charged again. Yet a few minutes later I look into my Appstore account and the upgrade was charged !!! This should not happen at all. I already requested a refund from Apple but this should not happen , its a hassle and I am sure I am getting a bad mark from the Apple guys !!! Very very bad !!!

From my experience, most times such things occur it is due to having switched your apple id. If you use(d) multiple accounts on your ipad, only one of them has the MG purchase.
(There is no way a user app itself can “see” what is going on the Apple ID level, the app can not see who is logged in)

This is not possible. It’s also nothing we developers even have access to:

When we submit an App to Apple, we just say to Apple that we want to sell an In-App-Purchase that is non-consumable (“A product that is purchased once and does not expire or decrease with use”).

Hereafter, everything that happens, is on Apples systems, according to Apples rules and we don’t even get to know if anybody make a purchase.