I did create a full explained tutorial about in app purchase in gamemaker .
Hope it will be usefull
link to my patreon page:
/ navidansari
timecodes:
0:00 intro
0:20 creat project in gamemaker
1:29 add and import google iap extension to gamemaker project
3:57 how to use iap extension in gamemaker
11:53 what problem can happen for you to get build failed and how to solved it
12:24 how to get name price currency and description of products in gamemaker