If you want to pay by credit card, please check that you have entered your card details correctly: the CVC number and expiration date. Secondly, check that you have sufficient funds in your account. Also, make sure you know your 3-D Secure password. This system is used by banks and credit card providers to provide more security for online payments. Incorrect answers to these 3-D Secure questions are the main reason for failed payments. You can contact your bank to learn more about how this system works.