Shop is not shown in Frames (X-Frames something)

Hello,

I have the problem, that my shop will not be shown in Frames... Google says it has something to do with a "X-Frames" Option. First I thougt it has something to do with the Provider, but he tested it and with an blank page outside Litecart the page is shown in Frames... so it has something to do with my Litecart installation.

Question: Is there something installed in the Script which is blocking the Frame?

Or is something wrong with my header? The only external Scripts are from Matomo and "Font Awesome"...

This is how my header looks like:

<title>xxx | xxx</title>
<meta charset="utf-8" />
<meta name="keywords" content="modellautos, modellauto, 1:87, h0, modellbau, modelleisenbahn, sonderpreise, gebraucht, zweite hand, alle marken, auswahl, autos, lkw, trucks, baumaschinen, feuerwehr, polizei, rettungsdienst, kran, tieflader, sattelzug, sattelschlepper, van, spielzeug, modelle, eisenbahn, modellbäume, modellhäuser, modellbauzubehör, trafo, led licht, pinsel, farben, haes, manufaktur" />
<meta name="description" content="Modellautoland - Gebrauchte Modellautos im Massstab 1:87 und gebrauchtes Modellbahnzubehoer">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="robots" content="index, follow">
<meta name="language" content="deutsch, de, DE">
<meta name="author" content="Modellautoland by HAES Modellbau Manufaktur Hamburg">
<meta name="publisher" content="Modellautoland by HAES Modellbau Manufaktur Hamburg">
<meta name="page-topic" content="Modellautos, Modellbau, Modelleisenbahn, Modellautosammler, 1:87">
<meta name="distribution" content="global">
<meta name="revisit-after" content="7 days">
<link rel="stylesheet" href="{snippet:template_path}css/framework.css" />
<link rel="stylesheet" href="{snippet:template_path}css/app.css" />
<link rel="stylesheet" href="{snippet:template_path}css/haes.css" />
<link rel="stylesheet" href="{snippet:home_path}ext/fancybox/jquery.fancybox.min.css" />
{snippet:head_tags}
{snippet:style}
<script src="https://kit.fontawesome.com/xxx.js" crossorigin="anonymous"></script>
<!-- Kundenservice Start -->
<script type="text/javascript">
  var _paq = window._paq = window._paq || [];
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u="//www.xxx.com/matomo/";
    _paq.push(['setTrackerUrl', u+'matomo.php']);
    _paq.push(['setSiteId', '1']);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
    g.type='text/javascript'; g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
  })();
</script>
<!-- Kundenservice Ende -->
</head>```

This is a CORS policy problem.

See this part
https://github.com/litecart/litecart/blob/dev/public_html/includes/library/lib_document.inc.php#L19-L21