When you're booking online, the Flexi fare option is one of the extras you can add. Most Business class fares are already Flexi fares, but sometimes there are discounted 'Business Saver' fares that are non-refundable and come with the Smart Saver rules.
Smart Saver fares are non-refundable, whereas Flexi fares are fully refundable. If you buy a Smart Saver fare and later upgrade it to a Flexi fare, only the upgrade portion will be eligible for a refund.
Name changes are not permitted on any fares, so you can't transfer them to another person.
Both Smart Saver and Flexi fares let you change your flights right up until departure. You'll have to pay any fare difference, and a service fee if not changing online.
For Smart Saver fares there's a booking change fee of NZD $100 per person (infants excluded), unless you're upgrading to Premium Economy or Business on the same flight. There is no booking change fee for Flexi fares.
If you don't show up in time for your flight, with a Smart Saver fare that sector of your journey will be cancelled with no refund. With a Flexi fare however, a no show is fully refundable.