If you try to get in a car park equipped with license plate reading, your license plate may not be recognised at the entrance (dirt, snow, faulty camera, etc.).
In this case, you can use the digicode or the QR Code, depending on the car park's equipment. The digicode or QR code can be seen in the details of your purchase.
At the end of your session, also use the digicode or QR Code to exit.