Vector 3s in zwift with Spinnig bike


I recently got a set of vector 3s pedals to put on my spin bike so I could use zwift. However the less resistance i have on my spin bike the higher the watts I see on zwift. If i have no resistance on could see crazy watt numbers, hit 1200 watts with no resistance, and no real effort. Could this be a problem with zwift or is it the pedals that are not measuring correctly? thanks