Reproducing the file_get_contents error while retrieving a waxlrs XML configuration

file_get_contents_waxlrs_xml.php

<?php 

$configuration_url = 'https://uomedtest.waxlrs.com/lti?u=https://uomedtest.waxlrs.com/embed/mostpopular';


$opts = array(
    'http' => array(
        'header' => "Accept: application/xml\r\n"
    )
);

$context = stream_context_create($opts);
$config_string = file_get_contents($configuration_url, false, $context);

/*
  file_get_contents produces this error:
  Warning: file_get_contents(https://uomedtest.waxlrs.com/lti?u=https://uomedtest.waxlrs.com/embed/mostpopular): failed to open stream: HTTP request failed! HTTP/1.1 404 Not Found in /var/www/html/test.php on line 12

*/
  
$config = simplexml_load_string($config_string);
$launch_url = (string) $config->children('blti', true)->launch_url;

echo $launch_url;

?>