Pat the drumsticks completely dry with paper towels. Season evenly with salt, black pepper, and onion powder.
In a shallow bowl, mix together potato starch, cornstarch, baking powder, paprika, salt, onion powder, and cayenne pepper.
In a separate bowl, whisk together the egg, soy sauce, and rice vinegar until smooth.
Dip each drumstick into the wet batter, letting any excess drip off.
Then dredge in the dry coating, pressing gently so it adheres well.
Lightly spray the air fryer basket with oil. Place drumsticks in a single layer (do not overcrowd).
Spray the tops lightly with oil.
Air fry at 400°F for 18–25 minutes, flipping halfway through, until golden brown and the internal temperature reaches 165°F.