Hello TGW
There is no need to enter / register your half fare card. All you have to do is to activate the half fare setting in your SBB Mobile app. Whether you are eligible to purchase half fare tickets is not actively checked during the purchase of a ½ ticket. This is the duty of the ticket inspectors on board the service.
To activate your Swiss Half Fare Card, it is necessary to initially activate the Half Fare setting in your personal information. How?
In the SBB Mobile app, when you are about to book tickets, on the screen with the ticket offers, click the pen icon. Then tick the ‘Half Fare Card’ checkbox, and save. The SBB Mobile app will update the ticket offers taking the half fare into account.
The same you can do for co-passengers: Open the SBB Mobile app, go to tab “Profile”, then select “Co-Passenger” from the menu. Add the passengers for which you want to purchase tickets, and activate the Half fare card option for everyone that will have one, or for children from 6 to 15.99 years of age.
See screenshots below.
Kind regards,
Roland

