expired Auckland SkyBus Airport City Express - Save up to $8 on Return Fare via Klook
I was a little sceptical about this at first since I had never used klook.com but tried it out, purchased a round trip ticket and had no issues.
Using the link you can get a single ticket for $15 (usually $18) or a return ticket for $26 (usually $34).
The ticket with QR code is provided immediately after payment in addition to being emailed to you.
I haven’t explored the rest of their site, will do another time but can recommend this SkyBus deal.