I guess this goes back to what security levels Widevine (the digital rights management) can ensure. If the Spotify app fails to request a specific level it denies it won’t download.
I keep forgetting specifics, but you could try searching for a liboemcrypto.so and remove it, seems to work for other (Samsung) users at
- S8: Onleihe App Audiobooks do not work - #8 by tcecyk
- Filme starten nicht in der App "Filmfriend" - #11 by tcecyk (in german, but still instructive)