Hello Llaloipough84
Since your understanding is incorrect, you have taken the wrong path and are about to purchase the Half Fare Card for residents, which requires much more administrative effort than the tourist version, the Swiss Half Fare Card.
You can simply create an account with SBB, stating that you do not have a customer number. As a tourist, you will not need a customer number. After creating an account, you can simply purchase the Swiss Half Fare Card. You can also download the SBB Mobile app and use the same username and password to authenticate yourself there..
https://www.swisspass.ch/register/1
In order to utilise your Swiss Half Fare Card within the SBB Mobile application, it is necessary to activate the ½ fare setting for each individual traveller. Please see the screenshots in this post to understand how it is done:
https://community.sbb.ch/d/26418-how-can-i-save-the-info-of-swiss-half-fare-card/2
If you want to bypass all the account stuff, you can simply purchase the Swiss Half Fare Card from the Switzerland Travel Center. There, no account is needed, on the other hand, when buying from them, the Swiss Half Fare Card cannot be seen later in the SBB Mobile app.
https://www.myswitzerland.com/en-ch/planning/transport-accommodation/tickets-public-transport/swiss-half-fare-card/
Please let us know if you have got further queries.
Kind regards,
Roland