In order to make your payment at Papaki via web-banking, use the Electronic Payment Code, which you find in the ordering email (or in the Control Panel if it is a service renewal / upgrading).
Specifically, the procedure you should follow is:
1. Login to Piraeus Bank web-banking.
2. In your account's administrative environment, select "Payments" in the menu that appears to the left and then "By category". After selecting the "Internet Services" category, find and select "Papaki" from the list as shown below.
3. After selecting the billing account, fill in your name, e-Payment Code and payment amount and click "Continue" to complete the process.