Hello Cielloickoi49
No, https://www.swissrailways.com/de is a reseller (agency) and the Swiss Half Fare Card is issued as PDF document yet simply works as fine as in the app.
The SBB Mobile app is not selling the Swiss Half Fare Card either, only the website sbb-tickets.cc/en. You have to create an SBB login (sbb-tickets.cc/en > Login > no customer account) before purchase. Only then you will see the Swiss Half Card in the SBB Mobile app, too (login with the same credentials).
To solve your issue: call your bank and tell them to activate the 3D secure ID, which is required for most European webshops, yet is often not activated for cards from the Americas as their security standard is lower.
Kind regards,
Roland