geofence to block the vehicle?
I ask because, we assume that the car is stolen and you don't want it to leave that specific area.
Yes, it is possible.
Sorry, I misread. It's not possible to do it for a specific geofence.
You could add the device to another traccar server where you only add that Fence and add the custom command
Is it possible to use a fence to block the vehicle?
"a specific Fence" and not all.