Android in-app, any examples?

Question

Android

Dear friends, I have repeatedly tried to approach the issue inapp, and all the time something does not work out or is not clear.
In Google it is not forgotten, but every second link has only a link to the official dock, and every third one does not carry a semantic load at all.
Please show some working example, where does the purchase check and the actual purchase process take place?
I would greatly appreciate a link.

Answer 1

A working example is just in the off-doc - https://developer.android.com/google/play/billing/...
All others may be outdated.
There is just a Purchasing item.
What is a purchase check - I did not understand, but it is also in the off. doc for sure.