DIAGNOSIS This is almost always caused by grease and food particles hardening in the basket rails after cooking, acting like glue.
FIX Do not force it. Unplug the unit. Pour a small amount of warm, soapy water along the top seam where the basket handle meets the main body. Let it sit for 5 minutes to soften the grime. Then, while firmly holding the main body, wiggle the basket handle side-to-side as you pull. It should release.
IF THAT DIDN'T WORK The basket or the internal guide rails may have warped from very high heat. Check for any visible deformation. If it's warped, you'll need a replacement basket from Chefman. For a non-warped but still-stuck basket, apply more warm soapy water and use a plastic spatula to very gently pry at the seam, focusing on loosening debris.
HEADS UP Prevent this by always removing and cleaning the basket immediately after use while it's still warm (not hot), and ensure the rails on both the basket and inside the unit are wiped down before reinserting.