If you have a fully open source product (with a permissive license) you can't just "paywall" it, as FOSS licenses allow you to build and often redistribute the product.

When you have a fully open source product and want to build a valid business model from it, you have to work WITH your license. The OsmAnd team chose an interesting way to do this by "paywalling" the Playstore version "OsmAnd+". But you still can get all the stuff, as it is open source.

A community-compiled version of the full OsmAnd+ named OsmAnd~ without Google Play services dependency is also freely available on F-Droid.

https://en.m.wikipedia.org/wiki/OsmAnd#Licensing

Welcome to the world of FOSS. 🌍