I'm trying to book BKK-CCU roundtrip on jetairways.com. After choosing the fare ("Promotional Fare"), I fill out my info and click "purchase," only to eventually get the error "Sorry, there has been an error in ticketing/processing your flight request. Your card is not charged. However, the amount blocked on your card will be automatically released by your bank. Please try again later."

I've tried two US-issued credit cards so far (Amex Plat and a Capital One Visa). Neither is billed when this happens. I know there are some issues with US-issued credit cards not working on Indian airlines' sites. I tried to book by phone but they won't sell me the "promotional fare."

So far nobody will explain what this error is, or whether it's a problem with the fare or with my payment method.

Are there any US credit cards that are known to work properly on jetairways.com?

And is it significant that the fares are always shown in THB for this route, no matter what country site I'm on?