Clean the chicken thoroughly and pat it very dry with paper towels. For thicker pieces, score the skin and flesh lightly to help the marinade penetrate and cook evenly.

In a medium bowl, whisk together the fish sauce, brown sugar (or honey), minced garlic, chopped red chilies, black pepper, vegetable oil, and sliced kaffir lime leaves (if using) to create the marinade.

Rub the marinade all over the chicken pieces, ensuring they are well coated. Place the chicken in a sealed bag or covered bowl and refrigerate to marinate for at least 30 minutes, or ideally 2-4 hours for maximum flavor. You can marinate it overnight if preferred.

Preheat your air fryer to 180°C (350°F) for 5 minutes. This ensures even cooking and crispier skin.

Arrange the marinated chicken pieces in a single layer in the air fryer basket. Do not overcrowd the basket; cook in batches if necessary to allow air to circulate properly.

Air fry the chicken for 20-25 minutes, flipping the pieces halfway through cooking, until the chicken is cooked through and the skin is golden brown and crispy. The internal temperature should reach 74°C (165°F).

Remove the chicken from the air fryer and let it rest for 3-5 minutes before serving. This allows the juices to redistribute, keeping the chicken tender and moist.