There are two methods to Void a Transaction:
If the Invoice has not yet been Posted, you can click on the small "Trash Can" icon to the right of the payment amount.
If the Invoice has been Posted, click the "Void" button in the Task Bar.
CheckIn will ask for confirmation, and then contact Payment Logistics to process the request.
You can confirm the status of the Transaction by clicking on the small "i" icon next to the payment amount.