Just spotted it on their blog!
$1 deals available from participating restaurants in Sydney on Tuesday 5th April 2022 only. $0 delivery fee; service fees may apply. Participating restaurants will be tagged in the Deliveroo app with '$1 deal'. Only 100 items available at $1 per restaurant, for up to one hour only, while stocks last. Participating restaurants will be named on Deliveroo_AU Instagram stories approx. 30 minutes before their $1 deals are made available on the app. Geographical restrictions apply - customers must be within ordering distance of a participating restaurant to access the offer. Only one $1 item can be ordered per customer from each participating restaurant. Delivery may take longer than stated in the app. Not available with other offers.