Debug uncompiled java plugin code instead of JAR

Not really an IONIC question but you guys might be able to help about.

I have to debug the official Phonegap Barscanner. However the plugin uses the final compiled JAR file which holds all the classes.

In Android studio I see the “reverse engineered” version of the code but breakpoints dont work here.

How do I include the code so that Studio is able to stop?

Thanks for any hints