Pedaling but 0 Watt, Speed, etc


I recently changed my tacx trainer to an 8 speed cassette after changing my bike. It was working fine before and was calibrated with no problems. Now after changing the cassette the software will not pick up any movement/pedaling from my bike - it registers as nothing, no watts, speed, etc. The app is connected via bluetooth and i have tried resetting the app, switching the trainer on/off etc but no success!

What have I done wrong?! please help :)