Using headset for Apps like Zello

Before the iOS 10 update I was able to use a Bluetooth microphone or plug in headset with a push to talk button for third-party push to talk apps like Zello without having to pull my phone out or have the screen on . Since the update, after the screen locks and I use the push to talk button, it starts playing music from my library instead of activating my push to talk app. How can I fix this?