Libgdx with In-App Billing V3

[progrmor]

Hello. My first thread on this forum!
Im currently working on a small project which include in app purchases.
Although, I can´t get it to work. To be brutaly honest, im completely lost.

Im using the Libgdx framework and that is what´s making it all very difficult. Cause I want purchases to made with the click of a button. And that button is located in another "project".
So what I figured was to use an interface playing as a middle hand sort of. This is what I´ve done: (Not sure if you prefer Pastebin or direct code?)
The class that holds the buttons = http://pastebin.com/tTrfXj1s

The interface =

public interface purchaseInterface{

public String TOMBSTONE_ONE = "Tombstone_one";
	
	//Request code for the purchase flow
	static final int RC_REQUEST = 10001;
	public void applyTombstone();
	
	
	
}

And the AndroidLauncher class =http://pastebin.com/xqn5LK8d

I get either NullPointer or nothing at all depending on how I integrate the classes and interfaces.

Thanks in advance!