Southern Ag's Liquid Copper (Is that what you used?) labeled rate for mangos is 4 teaspoons per gallon--- you used 6! Registered pesticide labels are incorporated in pesticide law. If you use registered pesticides, you must read and follow the label.
The Dawn probably increased the toxicity. Dish detergents are often played with in home plant remedies, and sometimes actually work, such as when used in tiny amoiunts with cooking oil (which sometimes kills both the bugs and the leaves); however, one doesn't normally recommend dish detergents mixed with registered pesticides, such as Liquid Copper.
For dissolving food-grade un-refined Neem Oil, such as Dyna-Gro Leaf Polish, you can use hot water with soy lecithin, and/or you can use hot water with Potassium Silicate fertilizer, of any brand, including Dyna-Gro Pro-TeKt. Or you can use Dr. Bronner's Liquid Bath Soap (which is true Castille Soap made of Potassium Salts of Fatty Acids, not a detergent), which actually has on-line labelling for use on plants and is exempt from registration. Any of these variations should probably be used as a separate spray--- I do not know if they would be compatible with Liquid Copper.
When you devise a new mix of your own, divide gallon rates by four to mix just one quart; put it in a spray bottle and spray individual twigs or small branches with leaves and watch for several days to see if damage occurs. Mark branches and note weather conditions and time of day. If no damage occurs, then you have a candidate mix to use on larger areas, to then see if it actually does some good.