- stripslashes: documentation ( source)
<?php
$x = '"<?xml version=\"1.0\" encoding=\"UTF-8\"?><checkOrderResponse performedDatetime=\"2017-07-09T16:11:52+03:00\" code=\"0\" invoiceId=\"2000729266842\" shopId=\"45951\"\/>"';
$data = new SimpleXMLElement(stripslashes($x));
echo '<pre>'.$data->asXML().'</pre>';