_paq is unresolved


I’m trying to track a link with the trackEvent feature of Matomo.
My code-snippet looks something like this

<li><a class="cite-record" data-lightbox href="<?=$this->recordLink()->getActionUrl($this->driver, 'Cite')?>"
           onclick= window._paq.push(['trackEvent', 'Clicks', 'Links', 'Matomotest']);"
           rel="nofollow"><i class="fa fa-asterisk"></i> <?=$this->transEsc('Cite this')?></a></li>

But my toolkit shows me that _pay is not known or resolved, and the tracking doesn’t work.

Does someone have a solution for my problem?

Best Regards,