The problem might be due to the fact that your bank does not use the 3D verification feature, which is a security tool for online payment; or there might be some compatibility issues with the version of the Mastercard you are using. In this case, in order to proceed, you may try to use a different Mastercard, and if the problem still persists, then you can go for an alternative payment method, which is swift transfer. But if you use this method, make sure you make your transaction using the correct account number and control number given in your payment bill during the application. Please do not make any payment without using the control number.