We periodically receive reports of people getting payment gateway or credit card validation errors, even when people are using credit cards which they regularly use on other sites and/or at real venues. This tends to occur more on non-U.S. cards. Recently, it's most often French Visas, but since other countries and cards have been declined as well, we haven't identified much of a pattern beyond that.
Particularly with French credit cards, some users have identified that banks have the following security requirements:
1 - validate a phone number to receive confirmation codes
2 - validate email address to receive confirmation codes
3 - make a least one physical transaction first (eg: buying stamps is a good candidate for a company)
Furthermore, instructions we've been given from our CC payment gateway as well as our merchant account bank are that people need to contact their individual banks when this happens, and probe about why this might be occurring. They have said the message returned is rather generic and originates from the card's bank, and the root cause must be found from them. Unfortunately, we are unable to contact those banks directly to find out why the cards were declined.
We apologize for this inconvenience.