Discount for specific services coupon

When running a promotion, say for 50% off Drone photos for June, would be great to create a code that applies to just that service/add-on. Currently, the codes apply to the whole order and so you would need to create a code based on dollar amount instead. Kind of the same, but maybe not as good, especially for those who have a different price for add-ons than stand alone services and still want to discount a %.

Just an idea.