Error Exporting My Animated File To .fbx


I’m still new to and I’ve created and animated a Shotgun I have made that I intend to import it to Unity. From what I have read you export animated Blender files to .xbf and that’s what I’m trying to do. However, when I attempt to export to .xbf I’m getting this error and I’m not sure how to get past it.

Any help would be greatly appreciated.

This is the .blend for my file
870animation.blend (1.35 MB)