Flex Tech Topdrive 50 does not start

Ahoi together! I bought the above-mentioned scooter for my friend to have something for the city. Now it’s the case that he sold me the box as defective, because obviously the generator would be defective. Today I built the device apart in the workshop and tried to provide the missing voltage from the generator by means of car battery. Unfortunately, the engine still doesn’t start. As far as I could see, the spark plug does not get a spark. why, that’s the question. I pulled off the spark plug and plugged in another spark plug, connected to vehicle mass and there was no spark, but the candle is definitely in order (checked at the spark plug center)! Therefore, I assume that the ignition coil does not generate high voltage. Does anyone have an idea where the error could settle? Please no comments on the quality of the scooter! That’s all there was, and at 80€ purchase price and 2700km I like to make something… MFG