How works app-in purchase

Hello. I need to know how work app-in purchase. I saw that I can use storeKit for IOS and another module (I cant remember it) for Android.

I wanna that the user can buy a digital producto and update a remote DataBase on a remote Server with the User Id.

Is this posible do it with that module?. How I should do this?

I would need get the user id from the device to compare it with the remote DataBase and active all the time the product in the app.

Thank you.