To void an invoice, open the Edit Invoice screen for the invoice you wish to void, navigate to the bottom of the screen, and click the "Void This Invoice" button.
CAUTION: Voiding an invoice will delete all of the events associated with that invoice from the Scheduler, and this action is not reversible. If a payment is applied to the invoice before the invoice is voided, the payment will become an open payment after the invoice is voided.
