Cassette not moving forward

Thanks for reaching out!

We will need more information to assist, and I'd recommend visiting your local bike shop or contacting Garmin Support for your region if an issue persists.

I suspect something was missed during initial set up, or there is an issue with the included freehub the cassette is mounted to.
For reference, please review our setup guide carefully:Setting up a FLUX Series Smart Trainer
I would also recommend removing and inspecting the freehub following the guide here:Maintenance and Care for a FLUX Series Smart Trainer

Without installing a cassette onto the trainer, you should be able to spin the freehub backwards (counter-clockwise) without much resistance, and you should be able to hear the freehub ratcheting like a standard rear bicycle hub.
To turn the freehub or cassette forward will require slightly more force, but you should be able to spin the large silver flywheel forwards by hand quite easily.