SamplePHPSubmissionCode.php

<?php
require_once "HTTP/Request.php";

$xml = "
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<order>
  <company-id>1</company-id>
  <shipping-profile>t1</shipping-profile>
  <shipping-full-name>John Doe</shipping-full-name>
  <shipping-care-of/>
  <shipping-address-1>123 Easy St</shipping-address-1>
  <shipping-address-2/>
  <shipping-city>Eau Claire</shipping-city>
  <shipping-state>WI</shipping-state>
  <shipping-zip>77593</shipping-zip>
  <shipping-country>US</shipping-country>
  <items>
    <item>
      <inventory-item-id>1</inventory-item-id>
      <quantity>1</quantity>
    </item>
  </items>
</order>";

$req =& new HTTP_Request("http://POST_URL_HERE/api/create_custom_order");
$req->addHeader('Referer', 'http://www.my_url_here.com');
$req->addHeader('Content-Type', 'application/xml');
$req->setMethod(HTTP_REQUEST_METHOD_POST);
$req->setBody($xml);

$response = $req->sendRequest();

if (PEAR::isError($response)) {
  echo $response->getMessage();
} else {
  echo $req->getResponseBody();
}

?>