A KeyCard is a pass with a square barcode that can be used to open the gates.
See the example below:
You need a KeyCard to pass through the gates if you do not have a square barcode or a working square barcode on your international ticket. You can get a KeyCard from the Train Manager on the international train if necessary. Do you need a KeyCard but haven’t received one? Go to the information pillar near the gates and push the blue button. The member of staff you speak to will be happy to help you. You can also approach a member of staff if they are present at the station.