If you want to do an online purchase of a SCNF (french national railway) ticket, the only option you get is: Pre-pay the ticket via credit card in their online store, and later pick up the ticket at some vending machine at the railway station.
So this is what I did for my Paris->Dijon travel. So I went to the first vending machine at the CDG Airport in Paris. For authorization you are required to enter the booking code, your name and the credit card you used to do the online purchase. The first machine was broken, since it wasn't able to read the magnetic stripe on my credit card. The second machine already had a sign attached that it is malfunctioning and cannot be used for pickup of pre-paid tickets. Al the other machines were out of service.
Then I went to the next machine and tried to buy a public transport ticket from CDG airport to Gare de Lyon. The fare is 8 EUR and according to the signs on the machine, you can pay cash (in coins, which I never have), by french debit cards (which I obviously don't have) or by VISA card. Unfortunately it refused to accept my perfectly valid VISA card. So I had to line up at the long queue in front of the ticket counters.
At Gare de Lyon, I tried again to pick up my train ticket to Dijon. Most of the machines would again have problems reading the magnetic stripe on the VISA cards, and the others could read it, but would just tell me: Cancelled, please retry at a different machine.
So I again had to line up for the extremely long queue in front of the ticket counters, wait in addition for the only English-speaking cashier to become available. I told her my story, and she said: Yes, it only works with french VISA cards.
I was outraged. The online shop for buying tickets is fully translated to English and German (among others). You can buy the ticket using a non-french VISA card, and the amount is charged to your credit card account at that time. The translated instructions tell you to pick up your ticket at the machines, and nowhere it was stated that you have to queue up in front of a counter with non-french VISA cards.
The sole purpose of reading the credit card at the ticket machine is to provide a third authentication factor ('is this person really the person who booked the ticket'). There is no technical reason for restricting this to credit cards of a particular issuing country.
I'm planning to write some letters about this, since this is actually against fair competition regulations. If I want to receive the same service and not wait for half an hour for every train ticket I buy than everybody else, I have to open an account with a french bank.