CMN.ATO.INCDTLS.000006: Payer's withholding payer number (WPN) is invalid validation error

The withholding payer number must be in the format 00 XXX XXX XXX.

If you're getting the CMN.ATO.INCDTLS.000006 - Payer's withholding payer number is invalid validation error, then you'll need to check with the Australian Taxation Office (ATO) that the withholding payer number (WPN) is correct and meets the ATO's withholding payer number algorithm requirements.