I have a 2014 prowler hdx 500. The transmission works in high and reverse but when I put it into low the motor revs at high rpms with a lot of grinding noise coming from underneath and it only moves about 2 inches.
That's not good, nobody is happy with 2 inches. I would inspect the shift linkage, confirm it's fully shifted in low. Cross your fingers and hope that's it, However it sounds like you stripped the low gear in the transmission box. I would search the web about if this was a problem with Kymco engines. I haven't heard of it happening before. The only common (relative) issue is going through belts prematurely.