GGB That is the classic profile of a margin problem rather than a sales problem. The money usually leaks through a few lines at once — food cost creep, labour scheduled to comfort instead of covers, rent that is too high for the revenue, and delivery commission the dine-in margin cannot carry. A structured read finds which one is costing the most.
From Restaurant Profit Margins in the UAE: What the Numbers Should Look Like — the full reading, with the method behind this answer.