Is it considered cheating to fulfill the request of restaurant owners to reduce the ingredients used in food when the platform applies discounts, and should this request not be met, and what is the expiation for what has passed if the action was wrong?

The buyer purchases the order with the specifications displayed on the platform and its discounted price. If the restaurant reduces the ingredients, it has cheated the buyer and violated the condition and contract. This is based on Allah Almighty's saying: (O you who have believed, fulfill [all] contracts), and His saying: (O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]), and the Prophet's (peace be upon him) saying: (Muslims are bound by their conditions). Cheating in sales is forbidden by the consensus of scholars, based on the Prophet's (peace be upon him) saying: (Whoever cheats us is not of us). What the questioner has done is the obligatory fulfillment of the platform's condition and giving advice to the buyer, and he cannot participate in cheating.