Nova Motors City Star 50 no power?

Good morning

I have a City Star 50cc scooter that won't start because it's not getting any power. The engine control light doesn't come on when I turn the key.
It started with the scooter simply turning off while driving and by “stepping” on the battery box it turned on again.

After starting it, which took a long time and a few attempts, it turned off again while driving and wouldn't start again.

I checked the battery to see if it was still charged enough. According to the charger, it was in the green zone. I changed the fuse in the battery but that didn't help either.
I don't know where to start.

mfg

Marcel