Pay with xxxxxx card / Pay with xxxxx bank account links are one time use links . You will be seeing this error if you click these links multiple times.
If you did not receive a confirmation email after clicking the links the first time you could do the following
Wait for a few minutes for the confirmation email to arrive
Pay using "PAY WITH NEW CARD " or "PAY WITH NEW BANK ACCOUNT" link in the email as these links do not expire.
You will be seeing this error if you are clicking on any of the Payment links within an email for which the invoice has already been paid . If you see this error it is a confirmation that the payment has already been made.
Please note that the above doesn't mean that the money has been transferred to the merchant.