Retr0id parent
You are correct
I believe that changed recently and Spotify started blocking the key requests from free accounts.
Then how do people with free accounts listen to music lol
(It is plausible they added some new DRM but it's not going to be anything too crazy)
Their official clients have moved over to playplay DRM protection for non-lossless files too. The old key endpoints no longer work for free accounts, they must have added a server-side check.