Hi Peter,
I had the same error, and I was missing the question mark after the 'js'.
The full script tag that works for me looks like this:
<script src="dist/index.js?{{cachebust}}" type="module"></script>
Hope this helps!
There is no template for index.html, but login.html has
<script src="js/login_i18n.js?{{cachebust}}"></script>
and this in the header
{{themecss}} {{appicons}} {{manifest}} {{startupimages}}