We tested our brownies with a store bought box brownie mix. The results turned out pretty good. But if you're using a homemade recipe, results can vary. Also, your specific model of air fryer will affect results.
Mix your brownie batter. We used this brand. It is the slightly small package which they suggest for an 8x8 pan (10.25 oz. instead of the usual 16-18 oz boxes).
Using a shallow air fryer approved baking dish, line it with foil. Mix your brownie mix and pour into the foil lined dish.
Air fry the brownies at 350°F for about 20 minutes. Using a toothpick, pierce the brownies. If you need more time, add additional 2-3 minutes at a time until brownies are cooked to your liking. Remove the brownies from the baking dish and allow brownies to cool.