duntruner Hi. Thanks for trying the Embed Gallery. Unfortunately, it is lagging somewhat behind the main Files Gallery and lacks sufficient documentation.
For starters, and you wouldn't know this, but you may need to use the Files Gallery version that is bundled with Embed, because current Embed isn't compatible with latest Files Gallery. So download the Files Gallery index.php from here instead please:
https://cdn.jsdelivr.net/npm/embed.photo.gallery@0.0.7/index.php
Now replace your gallerytest.php with the above, and I believe it should start working. Of course, you will have an older Files Gallery in place in that location, but the point here is to get Embed working of course. If you need to use Files Gallery also, you can always upload latest version in a separate location and point it to the same dir with the root config option. Let me know how it goes!
There are a few other issues you might stumble upon, but I think you should be able to get it working first.