This means that one of the safety switches is grounding the kill wire
So it is a mower wiring problem
Make sure you have the blades turned off.
If it is an electric PTO pull & push the switch a few times
There are few different switches, some are on relays & some are direct so we can not tell you anything more till we know the make , model & serial number of the mower that the Kwakka engine resides in.