You can add a payment without charging the guest's card on file (if they have one).
To do this, simply go to the guest's registration, and click the button labeled CASH or OTHER depending on what kind of payment you are adding. For this example we will use CASH:
Then on the next page, add the amount you want to charge. You can add comments to explain the context of this Transaction, and you can set the Fund Method.
Notice the default fund method was set to "Cash" but here are some other options you can choose from:
Now, save the Transaction, and this will add a payment transaction, without charging the card on file.