Thank you, solved!
Your code works perfectly. Thank you very much for the fast support!
Maybe this is something to add to the documentation, as a lot of users will have other languages than english.
It is possible in wordpress to only give the user access to their own uploads. So you can use the media library in frontend, without the user having access to all your files (your faq could mention this).
This makes the plugin work great in frontend, too, which will make it even more useful. I think you can improve your docs to show the real “power” of this great plugin.