Only available to "Sky customers". But anyone can enter the code during the online checkout to apply the discount.
Examples:
Order Price Per Pizza Normal Price Discounted Price New Price per Pizza 3 Lust Pizzas $17 $51 $34 $11.33
Order Normal Price Discounted Price 2 Lust Pizzas and 1/4kg Chicken Nibbles $42 $25
Terms & Conditions:
Only available to Sky customers. Applicable to online orders only. Not available in conjunction with any other offers. $25 minimum spend. Offer expires 6th September 2017. Promotion code must be used at the time of purchase to activate the offer.
I tried this a week or two ago. Was surprised when the Hell website said that no double pizzas count as part of the "spend $25". So instead of getting 2 + 1 pizzas, you'd need to get some other stuff to get the free pizza.