Love2d in-app products for android

[max973]

Hello everyone,
I need your help!
I would like to put a game with three levels in the google store of which the first level is free and the other 2 paid as in-app products.
I've been busting my brain doing research online about it for over a month without finding any clear explanation.
The main doubts are:
- Where should the Google Play Billing library be inserted? In the Android Studio Mainactivity file or directly in the Lua main?
- How can I let the main.lua file "know" that a level has been purchased and then use some simple code to unlock it (I use gamestates to manage levels)?

Thanks in advance and I hope someone can help me