Musescore Songbook can't open files offline

Hello!
I bought Musescore Songbook app for Android, basicaly because that would give me the option to see my scores offline. That's the main feature of the app.
And it is not working!!!
I can 'donwnload' the files from my personal account to my SONGBOOK, but once I'm offline I try to open the same scores and it gives me an error message: 'could not download file'.
???????
When I open the app online i can open my scores and it tells me they have been downloaded, but again I try to access them offline and it doesn't work.

Can anybody help me?
Or is the app a lie?