I am aware of the fact, that this is a very particular functionality, that deserves a profound introduction strategy.
Nevertheless: Please Apple. Getting my money is not BASIC programming à la IF - THEN - ELSE.
I buy the roasted chicken WITH ketchup. If you need further investigation on the ketchup - just sell the chicken with optional ketchup. I am not buying the "chicken with ketchup" at the price "with ketchup", if I finally may not get the ketchup at all. Please just add "mustard" if "ketchup" finally fails or takes ages to get delivered.