If you take payment on a ticket, you have to first return the items, then refund the amount paid, and then close the ticket. This will void the order.
For more information on refunds/returns, see https://rentitbizsoftware.freshdesk.com/solution/articles/14000056266-refunds-returns.
For more information on closing tickets, see https://rentitbizsoftware.freshdesk.com/solution/articles/14000056264-closing-tickets.