Hi again.
So, reading the https://matomo.org/docs/page-overlay/ page:

Page Overlay tries to load scripts and data from the URL you pass to the Matomo (Piwik) tracker. If you have a restrictive mod_proxy setup or there’s another reason why this doesn’t work, use the method setAPIUrl(apiUrl) of the Matomo tracker to let it know from which URL it should load the scripts and the data. The parameter apiUrl has to point to the root directory of piwik, e.g. http://piwik.example.org/ or https://example.org/piwik/. The call to setAPIUrl has to be made before calling trackPageView.

I set the snipped:

<script type="text/javascript">
        var _paq = _paq || [];
        var apiUrl = "http://internalaccess.sample.com/";
        /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
      _paq.push(["setAPIUrl", apiUrl]);
      _paq.push(['trackPageView']);
      _paq.push(['enableLinkTracking']);
      (function() {
        var u="//externalaccess.sample.com";
        _paq.push(['setTrackerUrl', u+'piwik.php']);
        _paq.push(['setSiteId', '23']);
        var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
        g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
      })();
</script> 

Now i have an error:

Uncaught ReferenceError: Piwik_Overlay_Client is not defined
at HTMLScriptElement. (piwik.js:41)

Any ideia?

Thanks,
TP

Thanks for contributing to this issue. As it has been a few months since the last activity and we believe this is likely not an issue anymore, we will now close this. If that's not the case, please do feel free to either reopen this issue or open a new one. We will gladly take a look again!