I suspect the error is caused by a permission issue.

Add the js file in “Jimdo” under “Custom Layout”/“Files.” Then copy the link (right-click - copy link) and paste it under "Settings"/“Edit Header” in HTML format (<script scr="..."></script>).

An example of a link: https://u.jimcdn.com/cms/o/abc...123/userlayout/js/script.js?t=123....890