You cannot completely prevent them from sharing it but you can make it more difficult. There is a share button on the back of the card which you can simply remove from the card. But if the cardholder browses their phone storage using file explorer, they will be able to locate the pkpass file and copy it and e.g. send via an email. If you want to prevent multiple people from sharing a discount voucher for example, we recommend making it one use only. You can also use identification elements on the card which you could verify when presenting the pass in person.