FBX 3D models often have flipped normals due to coordinate system mismatches between the source software and FBX’s default settings.
Normals (which tell the software a face’s "front" side) invert when exporting from a left-handed tool (e.g., Blender) to FBX’s right-handed system—this makes faces look inside-out.
To fix this, adjust the source software’s export settings (like "Up Axis" or "Flip Normals") to match FBX’s coordinates, or preview the model in a viewer before final use.