The solution proposed here works for me now. I was unable (or failed) to apply this configuration until now. But I'd call this a mere work-around. Until Spotify and Amazon work out their licensing deal for my region as well, this will do.
I did come to realize that when you link your personal Spotify account to your Alexa device (typically used by other members of the family) Spotify's restriction of allowing at most one device at the same time to be used for streaming with the same account is a bit of problem. To fix this I've linked the Spotify account of a family members that rarely streams music with Spotify