Each invoice is paid (closed) as it comes due. For financial reporting purposes, total accounts payable is calculated simply by summing the open (unpaid) invoices. Determining the liability due to a particular creditor, which may consist of multiple open invoices, is not such a simple task. The auditor should not assume that an organization using this approach would invest the time needed to respond to the confirmation request. Under such circumstances, the confirmation process would be ineffective.