It's mentioned in the the comments in this post: https://www.cheapies.nz/node/21419
There is no BOGOF code for Pizza Hut that i'm aware of.
They normally do promo codes for purchases over $8 but lately that's just been fries.
Dominos do a BOGOF promo regularly for some of their pizzas.
Check out the pizza page on this site for the current dominos deals.