Sometimes, a white window appears after you have entered your credit card information. This means that the payment is not successful. We are sorry for this inconvenience.
Payments may not go through because your bank and ours often get in each other's way. In this case we advise you to register your card in a PayPal account and then to pay like this afterwards.
Also, it may block if Adblock (or another ad blocker) is activated on your browser. This prevents payment windows from appearing. You can try turning it off.
Finally, if the problem persists, try switching to a different browser altogether. Try switching between Chrome, Mozilla and Safari.