Hello,
Please find the following code on the Page:
<button class="button button-3d nomargin" type="submit" id="template-contactform-submit" name="template-contactform-submit" value="submit">Send Message</button>
and replace it with:
<button class="button button-3d nomargin" type="submit" id="template-contactform-submit" name="template-contactform-submit" value="submit" onClick="ga('send', 'event', 'Anmeldung', 'Klick', 'Nachricht senden');">Send Message</button>
This should definitely work fine. Let us know if we can help you with anything else or if you find any further issues.