why cannot read a obj

[ckkcckk]

my code：
std::string obj_file_path = R"(D:\SCHOOL\Project Group\Data\Data_obj\Data\Tile_+248_-057\Tile_+248_-057.obj)";

open3d::geometry::TriangleMesh mesh;
if (!open3d::io::ReadTriangleMesh(obj_file_path, mesh)) {
std::cerr << "Failed to read the OBJ file." << std::endl;
return -1;
}

but it say
[Open3D WARNING] Read geometry::TriangleMesh failed: unknown file extension.
Failed to read the OBJ file.

Why，the extension is actually obj