You can do this subscription (24h) by yourself using the column to the right of the entrance door.
The best solution is to take some change with you (€ 10,00) and know the three numbers of your license plate.
Before insert in the column coins, you must enter the three license plate numbers even if your license plate has multiple numbers… remember the first three numbers.
With the credit card you have to do the same procedure and then enter the 3 license plate numbers and then insert the card in the appropriate slot, wait about 15 seconds and then with the blue button you will add € 0.50 of credit each time you press.
On the screen you will see both credit and the expire time of your subscription parking.