The DEFT reference number that your payers use to make their payments is generated by your software (or in residential real estate, downloaded from Macquarie Business Online by the agent). This needs to be provided to the payer, e.g. it could be printed on a levy notice or invoice.
The easiest way to determine the correct customer is to search for the DEFT Reference Number (DRN) that appears on your bank statement in your business management software. Our DEFT support team may also be able to help depending on the payment method.