This is to do with your airline, and you will need to get in contact with them regarding this issue. The flight that you are taking could be a co-shared flight that will land domestically at the next port and pick up the remaining passengers and become an international flight.
When passing through the immigration control point you must present your boarding pass that has a domestic sticker attached. You must sign the sticker and it must contain the serial number of the photo identification that you have used at check in.
A valid means of photo identification is either a current driver’s licence, a valid passport or another photo identification that is issued by an Australian State government or the Australian Federal Government for adults who are travelling. For children either a valid passport or a Medicare card can be used.