Diagnosis
This happens when food or grease gets down into the basket's track or grooves and acts like a glue, especially if it's cooled down after cooking. It's not broken, just jammed.
How to Fix It
Don't force it. 1) Unplug the unit. 2) Let it cool completely if it was recently used. 3) Take a butter knife or a thin, flat metal spatula. Gently slide the tip between the top edge of the basket and the body of the air fryer, right at the front. Work your way along the front edge, gently prying to break the seal. 4) Once you've broken the initial seal, you should be able to wiggle and pull the basket straight out.
If That Didn't Work
If it's truly welded on by baked-on grease, you'll need to soften it. Put a couple of inches of hot, soapy water in the basket itself (be careful not to tip it). Let it sit for 30 minutes. The heat and moisture will help loosen the gunk in the tracks. Then try the prying method again.
Heads Up
To prevent this, always pull the basket out and give it a quick wipe down while the unit is still warm after cooking. Letting grease and food residue cool and harden in place is what causes the jam.