For the last 15 years I travel through Paris each summer. About 5 years ago started having trouble at gar d'Austerlitz. Person swiped card 2 - 3 times and said it was not being accepted. Tried 3 separate bank Visa cards, same result. My wife is always in the country for 3 weeks before I arrive and she is using the same cards. So I know they work. I can take the same card and buy coffee at a kiosk. Of interest, the one time a credit card was accepted was by the conductor's mobile card device two year's ago (pay a premium on board). I have email exchanged with SNCF in french. They of course blamed my card. I suspect SNCF started rejecting foreign cards if their system doesn't receive instant response. They would rather have cash then pay the fee(?).