Hello Queeghuesu84
Does your credit card support 3D secure ID? It is a mandatory security element in most European webshops, also for sbb.ch. Talk to your bank if you do not have it. Or try another browser.
If it still does not work, try to purchase from here, the SBB & Switzerland tourism joint travel agency:
https://switzerlandtravelcentre.com/en/che/ticket/swiss-half-fare-card
Kind regards,
Roland
