TGV declines credit card purchase?

I had a lengthy discussion with my credit card company when TGV/SNCF declined a credit card purchase. Turns out that if TGV/SNCF processes the transaction as an ATM charge, it may be declined (could have something to do with choosing the option of "automated machine pickup" for the ticket but only TGV would be able to confirm that). I've purchased several tickets from TGV/SNCF online and the transaction was only declined when I opted for machine pickup. I hope this helps someone.