What do you promote without giving the bill away?

You promote the table that is empty, with the menu or the dish you already charge. A two-for-one or a gift that is not on the board and that the till does not know how to charge is not promoted. Point at the gap in the book, not at a cut. The ad gives away the dessert and on the floor that dessert is not on the bill. The ad for the gap, at the board price, with nothing added.