IonPopup.show not inserting options.templateURL into Popup body

[austingayler]

Template.asdf.events({
  'click [data-action="showReview"]': function(event, template) {
    IonPopup.show({
      title: 'Leave a review',
      templateName: 'reviewPopup',
      ...

and then reviewPopup.html is another Meteor template. No matter what I do I can't get that template inserted into the body. Documentation is kind of sparse on this specific option, is there something that I'm missing?

edit: title should be templateName