As Unity 3D is (mostly) not open source, Google must be working directly with the developers of Unity on the Android Game SDK.

Key benefits of Xsolla SDK for Unity include: Drop-in Unity Integration: Seamlessly integrates Payments, Web Shop, and other direct-to-consumer solutions into Unity projects with broad version ...

Through its Verified Solutions status, Bright SDK is featured on the Unity Asset Store as a best-in-class solution for game developers that are exploring non-intrusive monetization strategies.