Hello Ckiembodeaph59
You are talking about the Swiss Half Fare Card.
Make sure you are entering all traveller and credit card information in capital letters
Select the country of residence, change it to another country, and change it back to your country of residence. Some browsers have a problem with the country selection field.
Make sure your credit card supports 3D secure ID, otherwise the purchase is not successful.
Alternatively, purchase it at the airport; when doing so, it is delivered as a physical card not as an e-ticket, however.
Kind regards,
Roland