Sample POST request with Guzzle

guzzle_post.php

<?php

require 'vendor/autoload.php';

use GuzzleHttp\Client;

$client = new Client([
  'base_uri' => 'http://example.com',
]);

$payload = file_get_contents('/my-data.xml');

$response = $client->post('the/endpoint', [
  'debug' => TRUE,
  'body' => $payload,
  'headers' => [
    'Content-Type' => 'application/x-www-form-urlencoded',
  ]
]);

$body = $response->getBody();
print_r(json_decode((string) $body));