Yes, you can put stainless steel in an air fryer. However, there are a few things to keep in mind. First, stainless steel is a good conductor of heat so it will cook food faster than other materials. Second, stainless steel can be scratched easily so it's important to use a non-stick cooking spray or oil before cooking. Third, make sure the air fryer is big enough to accommodate the size of the stainless steel pan or basket you're using. Otherwise, your food may not cook evenly.