The best way to solve this is to make use of Network in Lighthouse (F12 in Google or Edge Chromium) and check the path the webbrowser is making use of finding config file

If there is no configUrl (pointing towards a configuration file) or baseUrl (pointing towards a gallery folder) in your gallery's embedding code, then Juicebox looks for a file named 'config.xml' in the same directory as the web page containing the embedding code.
If your gallery's configuration file is not named 'config.xml' or is not in the same directory as the web page containing the embedding code, then you'll see the "Config file not found." message.

You can either:
(1) Rename and/or move your gallery's configuration file so that it has the default name ('config.xml') and is in the default location (alongside the gallery's web page).
... or:
(2) Use a configUrl in your gallery's embedding code to point towards your gallery's configuration file, e.g.:

<script>
    new juicebox({
        configUrl: "path/to/my_own_configuration_file.xml",
        containerId: "juicebox-container",
        galleryWidth: "100%",
        galleryHeight: "100%",
        backgroundColor: "rgba(34,34,34,1)"
    });
</script>

Please note that if your gallery's configuration file is not in the default location, then you might need to adjust the imageURL and thumbURL paths within the file.

Another reason why you might be seeing the "Config file not found." message is if the file itself is somehow corrupt and the browser cannot read it.
Open the 'config.xml' file directly in a browser (drag and drop the file into a browser window or enter the address to the file into the browser's address bar) and you should see the XML code.
If there is a problem with the file (such as a control character in an image's caption which is breaking the XML syntax), then the browser should note the problem and the line in the file at which the problem occurs.
You should then be able to open the 'config.xml' file in a plain text editor and fix the problem.

I hope this points you in the right direction.
However, if you continue to experience difficulties, then please email me back with a link to your gallery so that I can see the problem for myself and hopefully help further.
Thank you.

Thanks Steven. Reason there was different code sent is I was playing around with different things trying to figure it out. So I tried both of your ideas below and neither got it working. Funny thing is though I am now longer getting the can't find xml error message on the QC page (with the embedded code). Nothing shows up now. I believe I have made all the necessary changes that need to be done. What I am doing is having a bunch of different city pages so need a gallery for each. Figured best way to go is have a directory for each city, hence the photogallery/quebeccity/ directory. The city pages reside on the root of the site. I have attached the xml file. Here is the embedded code. Sure it is just something stupid I am doing wrong.

<!--START JUICEBOX EMBED-->
<script src="jbcore/juicebox.js"></script>
<script>
new juicebox({
configUrl: "photogallery/quebeccity/config.xml",
containerId: "juicebox-container",
galleryWidth: "800",
galleryHeight: "400",
backgroundColor: "rgba(255,255,255,1)"
});
</script>
<div id="juicebox-container">
<!-- Image gallery content for non-javascript devices -->
<noscript>
<h1></h1>
<p></p>
<p><img src="photogallery/quebeccity/images/quebeccity1.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity2.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity3.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity4.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity5.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity6.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity7.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity8.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity9.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity10.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity11.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity12.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity13.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity14.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity15.jpg" title="" alt="" /><br> </p>
<p><img src="photogallery/quebeccity/images/quebeccity16.jpg" title="" alt="" /><br> </p>
</noscript>
</div>
<!--END JUICEBOX EMBED--><p>

Figured it all Steven, thank you!

I noticed in the embed code that this line

<script src="jbcore/juicebox.js"></script>

Did not point to the proper directory. I changed to read

<script src="photogallery/quebeccity/jbcore/juicebox.js"></script>

And now the error message is back again but only locally, works fine live. Which is okay with me. Cheers!