用php读取其余的已发送文件

i have a node js api that send file like this

exports.myFunction = function(req, res) {
   res.sendFile("path_to_file");
}

and in php i try to read the file received like this :

$client = new GuzzleHttp\Client();
 $res = $client->post('http://www.example.com',
 ['headers' => ['Authorization' => 'Bearer my token',
 'content-type' => 'application/json'
 ],
 'body' =>json_encode(['id'=>'5bf7c8cfe58e316de4d3ae89', 'type'=>'default'])
 ]);
 echo $res->getBody();

but i don't get the file, and i get this :

�PNG IHDR���f IDATx��w`U���of��g�zo �(�����O=���,�X���b�Į��N�қT!�PI