Hello RobDendle
Does your credit card use «3-D Secure Code» as a security element? If so, a page will appear during the payment process requesting identification (password, SMS, fingerprint, Face ID or Transactions App). This will clearly identify you as the cardholder. This pop-up window is automatically blended in by your credit card company and is not governed by the SBB. Many times, it doesn’t work because of that and also i would recommend you to change the browser.
It is not possible to use your payment card for bookings on sbb.ch/en. We recommend that you use a different payment card or that you purchase your tickets at your nearest railway station ticket office.
For further queries regarding payment using your credit card, please contact your credit card company.
Greetings, AuroraD.