Here is the response:
Request: Pickup_Postcode=4500&Destination_Postcode=2014&Country=AU&Service_Type=STANDARD&Weight=80&Length=430&Width=300&Height=140&Quantity=1
Response: charge=0 days=0 err_msg=Please enter a valid To postcode.
It seems to default to AU as the country even though NZ is selected.