I asked for this because we were recently working on a product which involved magstripe cards and banking and there it opened to me that to get the bank into your product (not technically, but by bank requirements and regulations etc.) is one of the moooost difficult things in world! because such products play with the "People's money" and that has to be secured, protected and governed by the banks, VISA, and the State itself.
That depends on the requirements of the project. If the project is willing to take the risk that when someone complains they lose the money there is no need for online validation.
I guess many companies (hotels for sure) still have the visa/amex papers and swipe through machine to pay off-line. This used to be the default way of paying but is now the back-up way.
That is why your name and card number is "embossed" (I don't know the English word but the letters are kind of pushed out of the card) and not just printed.
The electronic version of that is swiping through a magnetic reader.
The project takes the risk someone refuses to pay but it saves on development and connection cost with an increased customer satisfaction (no wait time). If you add a camera and keep the recordings you can show the credit card company who used the card in case of dispute.