You won’t get any indication from the car as it’s powered via the electrics from the van supplied from the socket-plug. The car doesn’t know it’s there so the green red lights are your confidence check facility.
It is not powered by the electrics of the van, the power come from the car's 12 volt sustained supply to the van. Hence why AL-KO require the car's supply fuse to be 25 Amp.
The red flashing indicates the unit has not parked its push rod fully back, so most probably the bakes are on or dragging if they had been set up okay, hence don't tow.
The solid red indicates it is not functioning, it is usually okay to tow like that, but without the advantage of its protection. It quite often clears a solid red if you pull forward a few metres.
IMO it is prudent to do that and recheck it has gone green.
Al_KO once and possibly still sell an in-car repeater of the LEDs.
IMO the only advantage of knowing it is "working" is that it has not failed to be armed and able to intervene, just as ABS etc.
It does not like these need to tell you it is doing its best to save you, that you ought to have twigged whist it is working.
Unless void of sensitivity whilst driving you ought detect its over zealous intervention that due to its very basic control system, it
can act on exiting roundabouts, or when the van rolls as you creep over a calming bump or rally field. "Can" not necessarily will, but if it does it ought to be noticed, IMO a comforting sign it is healthy.
This is a no frills system pared down to just do its job without undue complication, and void of the expense of complication.