Parent value string contains invalid character

Errr yeah thats super invalid HTML…

You need a page that containts

<script src="https://embed.twitch.tv/embed/v1.js"></script>
<div id="test"></div>

<script type="text/javascript">
  var parent = ['sites.google.com', 'www.gstatic.com', window.location.host];
  console.log(parent);
  document.getElementById('target_frame').setAttribute('src', document.getElementById('target_frame').getAttribute('src') + '&parent=' + parent.join('&parent='));

  var options = {
    width: 800,
    height: 500,
    channel: "monstercat",
    allowfullscreen: false,
    layout: "video-with-chat",
    muted: true,
    parent
  };
  var player = new Twitch.Embed("test", options);
</script>