Diagnosis
Polymerized oil and food residue. Standard detergents are ineffective once this coating bonds to the non-stick surface.
How to Fix It
Use a baking soda paste. 1. Mix 3 tablespoons baking soda with 1 tablespoon water to form a thick paste. 2. Apply paste to the stained areas. 3. Let it sit for at least 1 hour, preferably overnight. 4. Scrub gently with a soft sponge or nylon brush and rinse.
If That Didn't Work
For the main unit's interior cooking chamber, use the Airfryer's own cleaning function. Add 500ml water and a slice of lemon to the basket. Run the unit at 200°C for 10 minutes. The steam will loosen residue.
Heads Up
Never use steel wool, abrasive scrubbers, or oven cleaner on the non-stick coatings. This will permanently damage the surface.