I have checked the following:
The file is named pimform.dave.js and it is present in the siteassets folder in my on-prem SharePoint 2013 site. I have full admin permissions on the site. The file is present and can be downloaded by putting the URL in the browser address bar.
which is the correct URL.
What am I doing wrong? Searching this community site doesn't provide any hints. It seems like it should be easier than this.
Thanks in advance.