Wanna learn how to implement in app products purchase & subscription for android using Google's in app billing library without a third party library

Here is the link to implement in app purchase for products & subscriptions

I have implemented a tons of plugin like how to embed Godot game in native android app, react-native, flutter etc and implemented plugins like Text to Speech, Biometric like Face recognition & screen lock detection, Background location etc. Check here to learn more. I am planning to implement event more soon