When you open the vehicle with your badge, the box in the glove box will ask you for a 4-digit PIN code based on the dd/yy scheme (for example, if you were born on 24/06/1995, your PIN code will be 2495).
Please check that you did not make a typing error in your date of birth when you created your account.
If your PIN does not work, a message in the vehicle may tell you that your booking is complete, and that the doors will lock in 5 minutes. Simply exit the vehicle, lock the doors with your badge, then swipe the badge again to unlock the doors. This will reset your booking to 0 and you will be able to enter your 4-digit PIN again, made up of your day and year of birth.