Coat the BBQ rub around all the sides and bottom of the pork belly. Leave the fat cap uncovered, this is important for the fat to render and get crispy.
After that 20 minutes, the fat cap will begin to render and the salt will help the top get nice and crispy. Remove the pieces of pork belly temporarily from the air fryer.
Use a butter knife or pairing knife to scrape off the salt on the top of each piece of pork belly. Do your best to get a lot off before placing it back into the air fryer.
Turn the heat up on your air fryer to 425 F. Let it cook for another 8-10 minutes until the inside is fully cooked, the outside is crispy, and the fat cap is rendered.