Place the salmon in the air fryer basket and season with salt and freshly ground black pepper.
Cook at 200°C (390°F) for 15 minutes. This is usually enough for the salmon to cook through, but if you're using thicker slices then do check using a fork or a knife and see if it needs to be cooked for a couple of more minutes.
Take the salmon out of the air frying basket, and serve.
For the Garlic Lemon Butter Sauce:
Take a small saucepan and melt the butter. Add the garlic, and cook for 1-2 minutes until it's fragrant. Add the lemon juice, and vegetable stock and simmer until it reduces in half. Pour over the salmon when serving.
Don't overcrowd your Air Fryer. Make sure that the pices of salmon are not touching each other.
You don't need to preheat the Air Fryer. Just pop the salmon in the Air Fryer basket, set the timer and temperature and start.