Hello JAM70
Thank you for your message.
If you buy the Swiss Half Fare Card online at SBB.ch with SwissPass login, it can be displayed via SBB Mobile. To do this, log in to SBB Mobile with your login after the purchase.
Orders made without logging in or purchased on a website other than www.sbb.ch cannot be displayed in the SBB Mobile app.
When you purchase tickets afterwards, you can enter the name, date of birth and half-fare discount of the person travelling before the payment process. You will find this option in the small pencil before finalising the purchase.
Instructions and explanatory videos for the SBB Mobile app can be found here.
Have a nice day and a good journey.
Greetings TatianaR