In a medium bowl, whisk together 1/4 cup of the coconut flour with the baking powder, garlic powder, and xanthan gum.
Place mozzarella in a large microwave-safe bowl and microwave on high in 30-second increments until well melted and easy to stir.
Add the flour mixture to the heated mozzarella, then add the egg. Using a silicone spatula, work the flour and egg into the cheese, kneading the dough up against the side of the bowl.
Dust a work surface with the remaining tablespoon of coconut flour. Turn the dough out onto the work surface and knead with your hands until cohesive. If the dough is still very sticky, dust lightly with more coconut flour until it no longer sticks to your hands.
Divide the dough into 4 even portions and roll each portion out into an 8-inch log. Cut each log into 8 pieces.
Spray the rack of an air fryer with avocado or coconut oil spray (or brush lightly with the oil of your choice). Place the pretzel bites on the rack with some space in between each one, then brush with the melted butter. Sprinkle with coarse or pretzel salt and press lightly to help it adhere to the dough.
Air fry pretzel bites at 350ºF for 5 to 6 minutes, or until puffed and golden brown.
For the dipping sauce, stir the mayonnaise and mustard together in a small bowl until smooth. Serve with the pretzel bites.
Notes
Oven instructions
Set a baking rack over a baking sheet and spray the rack with nonstick cooking spray. If you have a convection oven, use that setting on 350ºF. If your oven does not have convection, set the temperature to 375ºF. Watch your pretzel bites carefully when baking, and rotate your pan at the halfway mark to ensure even browning. Depending on your oven, the pretzel bites may take anywhere from 7-12 minute to bake.