What version of the plugin are you using?

Hi,

Step 5 was missing one line of code. I've updated the article and will paste the code here:

/**
 * Step 5: Display the tab content via Javascript 
 */
add_action('wp_head', function() {
    ?>    
    <script type="text/javascript">
        (function ($) {
            $(function () {
                // Calendar 
                $(document).on('onEventToggleOpen', function (e, data) {
                    data.$instance.find('.stec-layout-event-inner-my-custom-tab').html(data.event.custom_input_name);
                });
                // Single Page
                if ($('.stec-layout-single').length > 0) {
                    $('.stec-layout-single-my-custom-tab').html(stecSingleEvent.custom_input_name);
                }
            });
        })(jQuery);
    </script>    
    <?php
});