getJSON & Mustache.js stopped working after ?callback=?

Question

I moved my JSON File to my http website and the getJSON & mustache stopped working after that.

I read that I should add ?callback=? to my json url. After that I can see something in the google chrome inspect network area. But still my json isn't rendered to html.

This is my code:

<main>

    <div class="container">

        <div id="stream"></div>

    </div>
</main>

<script id="live" type="text/template">
    {{#videos}}

        <h5>{{header}}</h5>

        <div class="card livestream"> 
           <iframe width="100%" height="100%" src="https://www.youtube.com/embed/{{url}}" frameborder="0" allowfullscreen></iframe>
        </div>

    {{/videos}}
</script>

<!-- Mustache.js -->  
<script src="js/mustache.js"></script>
<script>

        $(function() {

            $.getJSON('externalurl.com/events/json/livestream.json?callback=?', function(data) {
                var template = $('#live').html();
                var html = Mustache.to_html(template, data);
                $('#stream').html(html);
            }); //getjson
        }); //function

</script>