Companion tickets can be paid with airpoints :

"Airpoints™ members are able to purchase discounted tickets on an Air New Zealand operated international flights using Airpoints Dollars™. These are called Companion tickets and are available if you have already purchased a Business Class, Premium Economy, Economy Flexi (long haul), or Flexi Works and Flexi Works Deluxe (short haul) tickets."

The amount paid is differentiated by route and business/non business fares