Modifiers let customers customise a meal at order time: remove an ingredient (optionally changing the price) or swap it for a substitute ingredient / sub-recipe. They need the Meals Custom Modifiers module with Business: General > Modifiers Settings set to Recipe Swaps or Notes & Recipe Swaps (Notes only lets customers type a note; None disables everything). Accounts on the Base, Pro or Enterprise plan can also see the modifier editor in the meal form even without that module active.

Once enabled, every ingredient panel in the meal editor gets a Modifier section (see the next questions). If you click Add A Different Ingredient or Sub-Recipe Substitute without the module and setting both active, you get "This Feature is not Enabled, please contact support".