2016 Subaru Outback won't shut off audio book when answering the phone. Tech at Subaru dealership said it was because I was using one click digital and I needed to switch to audible. I don't believe that . And I won't take that for an answer, I think he just wanted to get me out of the lot.
This sounds more like a problem with the app then the Subaru audio system. I would try playing music or a different app and taking a call. If that works fine, you know it's a problem with the app.
A OneClickdigital Version 2.1 release document available here addresses problems people were experiencing during phone calls on Android devises. If you can update your app, that may solve the problem.
If it does not solve the problem, you may be left contacting the app developers, or finding an alternative like the Subaru tech suggested.