How to create in-app purchases for android?

Can anyone help me out how to create a working in-app purchase for android projects? I know there are many posts and questions about this in forum but it seems nobody really figured out how to create a working blueprint. The documatation also is not helpfull because it shows only a half blueprint and most nodes are not available for me for some reason.
If anyone knows how to solve this or have a working blueprint it would be exciting to post it here and help me out. Thanks :)!