It was well established with last year's Huawei P30/Pro discount (I think also with the Samsung and maybe others) that even if you received a discount for an interest free repayment schedule with a plan, 2degrees did not have any requirement to keep the plan for a certain period of time, or require you to repay the discount if you cancelled early.
There are currently two similar discounts for a variety of phones via PB Tech https://www.pbtech.co.nz/promotions/200-off-with-2degrees and 2degrees online webshop https://www.2degreesmobile.co.nz/mobile/phones/ Although they largely cover the same phones, they don't seem to be quite the same as for example the Nova 5T and some of the Oppo have a greater discount with PB Tech. Maybe Noel Leeming etc have the same thing, I didn't find it if they did.
Anyway the limited T&C provided by PB Tech and 2degrees just mentions repaying the balance. The only T&C I can find on the 2degrees website is https://www.2degreesmobile.co.nz/termsofuse/mobile/mobile-repayment-and-trade-up/interest-free-mobile-repayment-option-terms-and-conditions/ and only mentions repaying the discount for certain ancient phones. I think this is the same T&C we were dealing with last year and although it was updated in May last year and I don't know what changed but it doesn't seemed to have affected the discount issue, nor is there any mention of any ETF. And the pay monthly plan is still without any contract.
A PB Tech rep claimed on Facebook you need to keep the plan for 3 months or repay the discount, but then again I recall similar confusion last year. Have I missed something or is the situation still the same as before, i.e. you cancel on the first day of your plan if you want and keep the discount just repaying the remaining balance which includes the discount.
P.S. I did ask both 2degrees and PB Tech but from the experience of others last year, I wouldn't be surprised to receive confusing responses.