If approving an invoice that has already been paid, usually by an manual ACH or a Credit Card, you can "Mark As Paid" during the approval process.
An example would be if a General Manager uses their company credit card at Sam's Club for food purchases. The invoice still needs to be entered into the Invoice Inbox page with backup attached, but the invoice has already been paid, since it was an immediate purchase.
From Invoice Approval, you can click the triple dot menu on the top right of the page and select Mark as Paid.
From there, update the Payment Date and any notes.
The final step is in Payments. If it was marked as Paid, there's a final Approval step where you must Confirm this was paid. This is to ensure no invoices get posted and not actually paid.
Click the Confirm button to complete the approval process and move this transaction to the bank or credit card account.