Heading says it all, it's 10C discount on Z today. Though I coudn't see it on a Z site, local Z has 10c discount for all, event not a fly buys members.
10c Discount Per Litre at Z
60
Referral Links
Z App: random (17)
Referrer gets 1 free coffee (up to 3 max). Referrer requires referee's phone number.
Z Electric: random (2)
Referee gets 50L+ extra 25L. Referrer gets 50L. Referral code needs to be entered during account creation in the "Promo" section.
Related Stores
The links says "Swipe your FlyBUys card for an instant 10c off".
Maybe your local Z is matching a nearby station that has 10c off, therefore if you used your FlyBuys, you would get another 10c off?