Right-click and select Calculate new payment amount from the context menu. This will update the amount column on the payment line with the amount that is required to be paid. Note: If the amount being taken is different to the order total then, in edit mode, you can click on the manual payments check box to enter another amount. Take the payment manually (e.g. via a PDQ machine) and note the auth code).
Once the amount is correct then click back on the Edit button and make sure you are in the [ Sales Order | Payment ] tab.
Right-click on the credit card payment line in the payment grid.
In the context menu select Manual Authorisation Code.
In the popup enter the authorisation code.
Click on OK.
In the confirm popup click on the appropriate option either:
Yes to save now.
No to continue editing the order.
The payment line will turn purple and the code you entered will be in the Auth Code column in the payment grid.