Listly by Program Town
Here is the list of Top 6 Android InApp Purchase Tutorials/articles in java and kotlin
For Single Non-consumable one-time product
Java
https://programtown.com/how-to-make-in-app-purchase-in-android-using-google-play-billing-library/
5 For Multiple Non-consumable one-time product
Java
https://programtown.com/how-to-make-multiple-in-app-purchase-in-android-using-google-play-billing-library/
Kotlin
https://programtown.com/how-to-make-multiple-in-app-purchase-in-android-kotlin-using-google-play-billing-library/
For Multiple Consumable one-time product
Java
https://programtown.com/how-to-make-purchase-of-multiple-consumable-items-in-in-app-purchase-in-android-using-google-play-billing-library/
Kotlin
https://programtown.com/how-to-make-purchase-of-multiple-consumable-items-in-in-app-purchase-in-android-kotlin-using-google-play-billing-library/
For Multiple In App Subscriptions
Java
https://programtown.com/how-to-make-in-app-purchase-multiple-subscription-in-android-using-google-play-billing-library/
For Single Non-consumable one-time product