Hello Peterchen
First of all, hello 🙂
SBB sells hundreds of thousands of e-tickets every day. And in 99% of cases it works perfectly.
It is simply impossible to offer a shop that works from every place in the world, and with all devices and all browsers. Maybe the problem is with your device? Have you already tried the SBB Mobile App?
3D secure ID is a common security standard for European webshops; thus it does not need to be mentioned separately.
There is no obligation to buy tickets in advance, you can also buy tickets at the ticket machine or in the travel centre at the station, except for saver offers.
Kind regards,
Roland