Notice attached to invoice: operational creditor may apply under section 9 for corporate insolvency if debt unpaid within ten days. Notice attached to invoice demanding payment: an operational creditor must serve a dated written notice to the registered office of the corporate debtor attaching the unpaid invoice, specify the amount due, demand repayment and warn that failure to repay within ten days of receipt will enable the operational creditor to file an application before the Adjudicating Authority to initiate the corporate insolvency resolution process; the notice must be signed and include the authorised signatory's name, position and address.