Calendly Listener - GTM

<script>
window.dataLayer = window.dataLayer || [];
window.addEventListener('message', function(e) {
  var evt = e.data.event;
  evt && evt.indexOf('calendly') === 0 && window.dataLayer.push({
    event: 'calendly_booking',
    event_type: evt.split('.')[1]
  });
});
</script>