Excel is not exporting using php office in Laravel

Question

I am using PHPOffice for exporting excel in laravel it work fine on localhost but it gives me internal server error on live server error?

public function export(Request $request){
   $branchId =  $this->decryption($request->branch_id);
   $data = Reservation::select("id", "name", "contact","start_time","end_time","target_date",'weekdays')->with('pages',function($query){
                $query->select('pages.id','name');
            })->when($request->has('start_date'),function($query) use ($request){
                $query->where('target_date','>=',$request->start_date);
            })->when($request->has('end_date'),function($q) use ($request){
                $q->where('target_date','<=',$request->end_date);
            })
            ->where('branch_id',$branchId)->get();
        $data_array [] = array("name","contact","target_date","start_time","end_time","weekdays","page");
        foreach($data as $data_item)
        {
            $data_array[] = array(
                'name'      =>$data_item->name,
                'contact'   => $data_item->contact,
                'target_date' => $data_item->target_date,
                'start_time' => $data_item->start_time,
                'end_time' => $data_item->end_time,
                'weekdays' => implode($data_item->weekdays),
                'page' =>$data_item['pages'][0]['name']
            );
        }
         $this->ExportExcel($data_array);
    }

This funciton is used to export data which we have got from export function

public function ExportExcel($customer_data){

        ini_set('max_execution_time', 0);
        ini_set('memory_limit', '4000M');
        try {
            $spreadSheet = new Spreadsheet();
            $spreadSheet->getActiveSheet()->getDefaultColumnDimension()->setWidth(20);
            $spreadSheet->getActiveSheet()->fromArray($customer_data, NULL, 'A1');
            $Excel_writer = new Xls($spreadSheet);
            header('Content-Type: application/vnd.ms-excel');
            header('Content-Disposition: attachment;filename="Customer_ExportedData.xls"');
            header('Cache-Control: max-age=0');
            ob_end_clean();
            $Excel_writer->save('php://output');
            exit();
        } catch (Exception $e) {
            return $e;
        }
    }`

This is what i am getting error at the end in respose

status code :502
{
  "message": "Internal server error"
}