Hi @dj_datum ,
You need to include html in handlerbar script tag itself, if you are trying include inside script tag then it will not be evaluated & included as html file. please check below code.
<script id="modal-popup-id" type="text/x-handlebars-template"
data-sly-include="/apps/{project}/{file location}/modal-popup.html">
</script>
Include html file in Modal Popup html:
<div class="modal fade" role="dialog">
<div class="modal-dialog">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal">×</button>
<h4 class="modal-title"></h4>
</div>
<sly data-sly-include="/apps/{project}/{file location}/popup-body.html"/>
</div>
</div>
Hope this helps!