Hello Right Person
You should not add the Half Fare Card option in your traveller details if you are about to purchase the Swiss Half Fare Card. This could lead to some system confusion… Uncheck that setting, purchase the Swiss Half Fare Card setting, and activate it again.
If it still does not work, you could purchase the Swiss Half Fare Card from the Switzerland Travel Center (STC), the SBB travel agency. The only downside, it will not appear in your SBB account if you purchase it from the STC.
https://switzerlandtravelcentre.com/en/che/ticket/swiss-half-fare-card
Kind regards,
Roland