Hi Mohamed,
The issue only occurs when the order is completely finished. When the customer want's to pay later (after receiving an design example from me first), then he/she Logs in on the clientside and normally has the option to pay under "orders". Here they can change the way of payment too. But this is not working anymore. I have the options "allow clients to change their payment method after purchase" and "allow clienst to pay later" both checked in the configurationtab as you can see in the last screenshot.
Problem SOLVED together with the pdf attach plugin problem.