Although my card is valid, the online system does not accept it. Why not?

If you have received a message from the organisation saying that your VISA or MASTERCARD has not been accepted, even though it is valid, your bank or savings bank probably has a system for checking identity beforehand in order to make safe payments. Your bank considers this security system to be indispensable for permitting online payments and, if it is not used, your payment will be refused. More and more financial organisations use such systems. More information at Ticketea.