Content view reports empty


Hello. I’m trying to get info what part of my long page is viewed by visitors.
On my page I added this to my links:

<a … data-track-content data-content-name=“Number N” data-content-piece=“Thumb”>

Where N is 10 20 30 and so on moving down the page.

Matomo tracker code is:

<!-- Matomo -->
<script type="text/javascript">
  var _paq = window._paq || [];
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  (function() {
    var u="//<?=$_SERVER['SERVER_NAME']?>/matomo/";
    _paq.push(['setTrackerUrl', u+'piwik.php']);
    _paq.push(['setSiteId', '3']);
    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.php'; s.parentNode.insertBefore(g,s);
<!-- End Matomo Code -->

When I scroll my page down I can see http requests (using HTTP live headers plugin) to my Matomo server for each 10th link, but this site Contents report is empty.

What did I wrong?