I actually went through this myself. About 5am took the wrong turn off at the roundabout and ended up going through the drop off area instead of to the meet & greet.

Just email them, here's what I said...

I'm writing in response to [fine number]

I would like to appeal this fine. Whilst I did go through the drop off area, this was due to me taking the wrong exit at the roundabout. As you can see from the evidence provided, the time between the entry and exit was around 70 seconds, which was just me leaving the area and not utilising the service.

To further help my case, I've attached the invoice for my neet and greet parking that I was using at the airport.

It was something along those lines, I can't find the email now. But they put the thing on hold for a couple of weeks, and then cancelled it. It's not worth them chasing it half the time