Garmin Speed and cadence 2. Paired but avatar doesn’t move

Hi all

I’ve got a garmin speed and cadence 2 with a basic giant mag tron trainer. I have the Zwift app on my IPhone 11 and when connected through the Zwift the speed and cadence is connected. However when I’m cycling my avatar remains still. Anyone know how to get around this and is the only way getting the Ant+ device ?