Bring a large pot of water to a boil and boil the pork belly skin side down for 3-5 minutes until the skin is fully cooked.
Remove the pork belly and allow it to cool enough to handle. Use a sharp knife and scrape the surface of the skin to remove any hairs and impurities. Rinse the pork belly and pat dry with paper towels.
Fan out 3 toothpicks and pierce the skin all over, making hundreds of tiny holes along the surface of the skin. Be careful not to pierce into the fat layer
Flip the pork belly over skin side down and cut slits into the meat about halfway down. Make each slit 1-1.5 inches apart, lengthwise and crosswise, forming a grid pattern.
Combine all the RUB ingredients in a small bowl and mix well. Generously massage the RUB mixture onto the meat only, not the skin. Be sure to cover the sides and get into the slits.
Place the pork belly skin side up onto a large piece of foil and wipe off any rub. Fold each side of the foil up the edges so that it is flush with the skin.
Sprinkle salt over the skin and let it sit for 10 minutes. With paper towels, wipe off the salt along with the moisture the salt has drawn out.
Use a basting brush and apply a layer of white vinegar on the skin. Be sure not to let the vinegar drip down the sides.
Refrigerate the pork belly uncovered overnight.
Place the pork belly with foil in the air fryer and cook at 400°F for 20 minutes until the skin becomes bubbly and golden brown. Turn the heat down to 300°F and air fry for another 15-20 minutes.
Let the air fried pork belly rest for 20 minutes. Slice and serve.