I pre booked my parking on line before arriving at the airport as I was travelling for business purposes therefore my employer was paying for it. When I went to exit the barrier the machine said I needed to pay an additional £39 for my parking. I had to go to the machine and pay again for the parking I had paid on line! I couldn't remember the exact arrival and departure times I stated therefore I couldn't really argue at the time and as it was 11pm I just wanted to get home as I had a 2 hour drive Since returning I have checked and did not over stay my times so Im still not sure why I had to pay again