Swiss Travel Pass - can't complete online purchase

SBB uses 3-D security, like Master Pass or Visa Checkout for on-line transactions. Then during the purchase, they come back to you to enter your PIN. You have to regiter your card in advance and get a PIN. I have heard that American Express Card also works. You can also register and use the SBB app. Finally, unless you will be using the STP on a train as you enter Switzerland, you can buy it at the airport train station or any full service Swiss train station. There will be no credit card hassles with a face-to-face transaction.

Your credit card probably needs 3-D Secure aka Verified by Visa/Visa Secure.
Though you might try buying it on the ap.

To tell you the truth there really is no advantage to buying it before you get there; it is real easy to buy it when you get there.
What if your flight is delayed a day then you would lose value on that 4 day pass.
Both Zurich and Geneva airports have SBB offices open early to late.

As far as buying the Pass after I land in Zurich, what happens if my flight is delayed - I think the office that sells the Passes closes at 6:30 pm ??
Thx for the very prompt responses.

PS
I need to get from Zurich to Basel on the first day.

None of my credit cards worked EXCEPT my American Express.

The SBB office in Zurich Airport is open til 21:00. The last train to Basel is at 23:00

Actually, the airport ticket office is open until 22:00 unless its a public holiday.
https://www.sbb.ch/en/station-services/railway-stations/further-stations/station.3016.zuerich-flughafen.html

We land at 3:45 pm, so am much relieved with your info on the extended hours.
Thanks

When trying to purchase any tickets from an overseas site, my CC company sends me a one time code to complete the “secured by visa/MasterCard” transaction.

IIRC, using Apple Pay from my phone when buying train tickets at the kiosk made it so I didn't have to mess with w PIN.