when call qrencode_save,return 502 bad gateway

$qrcode_image = "/tmp/qrencode1.png";
$content = "hello world";
try{
    $resource = qrencode_create($content, 2, 2);    

```
qrencode_save($resource, $qrcode_image);
```

}catch(Exception $e){
    print_r($e->getMessage());
}

i don't know why
