I want to use Runtastic on my Apple Watch, but I can't get it managed to have the audio feedback / music playing on the Bluetooth headset (Plantronics Back Beat Fit). As soon as I start the workout, the complete Audio feedback is on the iPhone speaker. If I put the iPhone away (i.e. flight mode), Runtastic prompts that the workout can't be started because the iPhone is missing. I have to say that the BT connection and music playback with the Watch built in Apps work very well. I tried to reinstall the iPhone and Watch app, but that didn't help. What is wrong?