FBX 3D models often have flipped normals when exported due to coordinate system mismatches (e.g., Z-up in Blender vs. FBX’s Y-up default) or unrecalculated normals after editing.
Coordinate system clashes reverse face orientations—FBX expects Y-up, so Z-up from tools like Blender can flip normals.
Unrecalculated normals: If you edit the model without updating normals, their correct direction won’t transfer to the FBX file.
To prevent this, set your export “Up Axis” to Y-up and use your software’s “Recalculate Normals” feature before exporting.