My preview mode is not working

If you send me the file you are trying to preview, I can try to reproduce the problem on my device.

I sent the file to the in app tech support email. Is that okay?

I took a quick look. Please make sure to use relative paths when referencing files in the same directory.

For example this won't work in the web preview:

<script src="/index.js" type="text/javascript">    </script>

Instead use:

<script src="index.js" type="text/javascript">    </script>

Also, there is this comment in the file:

This HTML file is a template.
If you open it directly in the browser, you will see an empty page.

You can add webfonts, meta tags, or analytics to this file.
The build step will place the bundled scripts into the tag.

To begin the development, run `npm start` or `yarn start`.
To create a production bundle, use `npm run build` or `yarn build`.

So not sure if you actually can preview this file directly. 

There are also placeholders like "%PUBLIC_URL%" in the file that won't work when you preview the file directly without processing.