Zwift cog, no resistance

I have bought and installed a new cog, I have updated everything but it gives no resistance . I can easily go 8 kg/kg without any effort

That sounds like a problem with the trainer reporting incorrect power numbers. The cog is just a cog, a piece of metal with no electronics in it. It’s not really different from riding with a cassette shifted to the 14t sprocket. What’s the trainer?

Hi and thanks!
I have an Elite Suito-T, I think you’re right because I’ve had the same problem when I do a workout session, no physical resistance, but when I bike with my “own gears” everything works fine.
Thanks Paul

I’m not sure I understand the problem you’re describing. When you have the Cog on the trainer, I wonder if the freehub is properly seated in the trainer - does it spin forward freely with your hand? It should only spin freely in the reverse direction (freewheeling).