You're right that buying fuel at Ampol does require you having a dual doctorate in astrophysics and atomic/nuclear science before even leaving home. Ampol's idea of retailing must be the most complicated and convoluted in the history of all that's unholy.
Whilst they're all branded Ampol, there are so many different flavours of Ampol that I challenge anyone to be able to understand and keep up with it.
Ampol stations can be either Ampol or not Ampol, but no-one can tell because they’re all branded Ampol
Ampol stations can accept Everyday Rewards or not accept Everyday rewards, but you’ll never know until the cashier rejects your card
Ampol stations that do accept Everyday Rewards may only award points but not accept the fuel discounts, but again, you’ll never know until you try and then get rejected
Some Ampol stations that do accept Everyday Rewards will both earn the points AND accept the fuel discounts as well, but these are as rare as rocking horse cough and if you find one, you should immediately buy a lottery ticket as well just in case
Some Ampol stations accept Ampol FuelPay phone app as well as Everyday Rewards points and Everyday Rewards fuel vouchers AND they also participate in Amex Offers as well, but these are basically unicorns and it’s easier to just assume they don’t actually exist in the real world.
Some Ampol stations (generally those that are not real Ampol stations, just branded Ampol) will accept Woolworths Gift cards for payment and others will not, but again you won’t find out until the gift card gets rejected and you find you can’t pay.
If that isn’t enough permutations, then there is also the payments methods to consider as well. Some Ampol stations will accept Amex and Diners Club cards, others will not. Some will surcharge for credit card use and others will not.
I basically give myself 30mins to work it all out before even starting the car. Buying fuel at Ampol is not something anyone should ever do on a whim or without significant advance pre-planning.