How can I intergrate Payworks in my Xamarin.Forms app (PCL)?

Hello together,

I want to use payworks (http://www.payworks.mpymnt.com/) in my Xamarin.Forms App, because I don´t want to build two separate apps.
First I started with Android and created "my" payworks app with the solution from the link in Android studio. This works fine.
But how can I now integrate this Android project in my Xamarin.Forms App (in PCL)?
If I try to bind the project as a .jar, is this possible with pcl and can I use all references which are used in the android payworks app?
How is it with Java Native Interface? Is this the better way?
Or is there a third much better solution?
I don´t want to waste too much time with the wrong way, therefore I need your help.

Thanks for all!

Pete