Class has unknown base type. Binding java library to Xamarin project

I'm trying to implement the Personal monetisation service SDK( downloaded arr file from their site) to my Xamarin Forms app. I do all as it described in Xamarin manual, but the Visual Studio cannot correctly transform SDK written on Java, to my Binding library. I received lot warnings like Class X has unknown base type XX. I looked inside aar file, the needed classes had chain of extensions but VS can't convert it. Now I stuck, and would be thankful for any help.