This is what you do when you have pre-booked a parking space.
At the entrance
Drive up to the entrance gate of the car park you booked
Hold the QR code for your booking up to the QR reader at the entrance.
Your booking is scanned and checked.
The gate goes up.
At the exit
Drive up to the exit gate.
Hold the QR code for your booking up to the QR reader at the exit
The gate goes up.