Issues with Magene speed and cadence sensors

Hello dear community,
I am new to Zwift and have purchased Magene speed and cadence sensors. They do connect with Zwift, I tried both ANT and BT connections and in both the speed that shows up on the Zwift app is not really the same as in reality. The sensors work, because when I ride outside they connect to a cycling computer and show the correct speed. I tried also to switch between devices, i.e. run Zwift on my laptop, my tablet and my phone.
Any of you can think of why this is happening? anyone else here uses Magene?

Thank you