golden eagle

I'm brand new to motor bicycling. I have a sixthreezero evryjourney bike (https://www.sixthreezero.com/products/evryjourney-mens-touring-hybrid-matte-black), I want to install a 49cc or less kit. I've been looking at KMB, BikeBerry, and most recently, Golden Eagle. I'm trying to compare a kit...

I have just installed a 32 cc 4 stroke on my 26 in mountain bike--kit purchased from Golden Eagle. I find that the kevlar drive belt slips now and then--more frequently than I'd like. does anyone else have this problem or have they had it and found a way to resolve it? Any tips will be greatly...