There is at the moment an unknown error in our credits payment system affecting only users from France who are using Societe Générale bank.
The credit card transfer fails as the 'verified by visa' authorization is not cleared for some reason, and you cannot complete the Credits purchase. We apologize for the problem and we are attempting to sort it or provide more information on monday when the payment processor's support is available to us. In the mean time you can also use PayPal to make the purchase.