Thank you for the login details. The FTP was not working, but it wasn't needed.
The problem was that the shortcode was placed into a “Custom code” block on the front-page visual editor. I hope you don't mind, but I have changed the type of that block to simply “Text” and put the shortcode there: https://i.imgur.com/QJJao41.png
Now it appears to be working correcly.
If you like my products, don't forget to rate them on codecanyon :)