로컬에서 업로드하면 잘되는데...

호스팅하고는 안되네요..ㅠㅠ css파일은 잘만불러지는데..

왜 파일업로드가 안되고 null이되는지...

$config['upload_path'] = '도메인/upload';
                $config['allowed_types'] = 'gif|jpg|png';
                $config['max_size'] = '2048';
                $config['max_width'] = '1600';
                $config['max_height'] = '1200';
                $this->load->library('upload', $config);
                
                $this->_aheader();
                if (!$this->upload->do_upload('URL')) {
                }else{
                    $data = $this->upload->data();
                    $filename = $data['file_name'];
                    $url = '도메인/' .$filename;
                }
                $this->form_validation->set_rules('IMG_TITLE', '제목', 'required');
        
                if($this->form_validation->run() === false){
                    $this->_referenceAddImg();
                    $this->_afooter();
                }else{
                    $this->admin_model->addIMG(array(
                        'IMG_TITLE'=>$this->input->post('IMG_TITLE'),
                        'IMG_CONTENT'=>$this->input->post('IMG_CONTENT'),
                        'URL' => $url,
                        'REGDATE'=>$this->input->post('REGDATE')
                    ));
                    echo "<script>alert('이미지 등록 성공');</script>";
                    echo "<script>location.href='/admin/reference/imgList';</script>";
                    exit;
                }