Found this completely by accident. If you load https://www.qantas.com/nz/en.html, and then switch tabs and come back, maybe wait a bit, and a popup appeears:
Sign up. Take off $30.
Sign up to Qantas Red Email and save $30 per booking on your epic adventure. Plus, be the first to receive the latest travel deals. Offer available for new subscriptions only. Conditions apply.
Subscribe now
That then took me to https://www.qantas.com/nz/en/travel-info/email-subscription.…
Sign up to Red Email and save $30 per booking on your epic Aussie adventure.
Conditions apply. New subscribers only. Limited to eligible bookings made by 11 December 2023.*
You can just scroll down the page and find where it says Red Email.