XML : Proper way to send (POST) xml with guzzle 6

I want to perform a post with guzzle sending an xml file. I did not find an example.

What I 've done so far is :

  $xml2=simplexml_load_string($xml) or die("Error: Cannot create object");  use    GuzzleHttp\Client;  use GuzzleHttp\Psr7\Request;  $client = new Client();  //  $request = new Request('POST', $uri, [ 'body'=>$xml]);  $response = $client->send($request);   //  //$code = $response->getStatusCode(); // 200  //$reason = $response->getReasonPhrase(); // OK   //   echo $response->getBody();    

No matter what I try I get back error -1 which means that xml is not valid. XML that I send passes online validation though and is valid %100

Please help.