2016 Craftsman YT3000 lawn mover

My mower runs and the blades will engage but the mover will not move. I have the engagement lever (on the back of the mover in the correct position). The drive belt has tension but doesn’t rotate when the mover is put in gear (forward or reverse) The level to engage the drive (forward/reverse lever) seems to work and move the proper levers on the transmission.
This happened while mowing. The mower just stopped moving.
Any suggestions?