It's 50% off the base price, which excludes the delivery fee, the convenience fee, the inconvenience fee, the COVID recovery charge, the Livable Wage surcharge etc.
The last time I ordered UberEats, all the fees plus tip nearly doubled the cost of my order.
Open two windows, apply the coupon in one. Watch as the order totals are not 50% apart. They instantly jack the service fees on the 50% coupon order.