Specifying a partnerId.

gistfile1.html

<a id="tbd-btn-1" href="#">Go with friends</a>

<script type="text/javascript" src="https://js.thebestday.com/v1.js"></script>
<script type="text/javascript">
  var openModal = function() {
    var plan = new theBestDay.widget.Plan({
      title: "Surry Hills Lunch Time"
    });

    var modal = new theBestDay.widget.Modal();
    modal.open({
      plan: plan,
      partnerId: "1"
    });
  }

  var btn = document.getElementById('tbd-btn-1');
  btn.addEventListener('click', openModal);
</script>