In the play a lot of apps pozhertovaniya developer on program development or expression of gratitude.
But rereading https://play.google.com/intl/ru_ALL/about/monetiza...The payment system of Google Play content not supported for the following types of products and services:
A one-time transfer of funds. These include loans, online auctions and donations.
or in the English version
One time payments, including peer-to-peer payments, online auctions, and donations.
Has "buy me a coffe" it is a violation or not ?
Or forced into
Additional features or special content. For example, the ability to view the app with no ads
or features that are not available in the free version.