I noticed last week, that in some stations, the doors are all closed and you can only open them by checking out with a chipkaart or a printout with a QR code. So, what if I arrive there and my ticket does not have a QR code? For example, because I travel from abroad and the tickets sold in the machines of Deutsche Bahn don't have such a code? Is there a way to open the doors? Or am I supposed to climb?