First follow the payment link, provided in the email notification. You should be redirected to Secure Checkout page, where you need to switch the currency to USD:
Now procced to Billing Information page:
Enter your billing information in appropriate fields and click Payment Method when you're finished:
Switch to PayPal tab and :
You'll need to either have a PayPal account or apply for one:
Then enter your MasterCard information.
MasterCard via PayPal should work properly. Please contact us in case of both success or failure. In case you succeed with payment via PayPal, we'll cancel the previous order that had MasterCard on file and caused 2CheckOut to send the misleading notifications.