Finally! This was the answer:
Create a directory for it through the File Manager. For example create /app/data/catalogs/music. You can upload new audio files to this folder now or later.
Kind of new to Linux, do not know anything about docker yet. But after following your reply, it finally worked!
I'm now going to delete it all, and re install to learn more about it.
Thank you very much for your reply, much appreciated.
Now I do not need a tall tree with a short rope, I can go for the short tree with the long rope! 🙂
Chris...