Apparently Spotify deprecated the trackset feature of it's embedded play button last July and recently disabled it completely (they removed it after 9 months and yet they still use a Last.fm API that was deprecated 8 years ago...).

Unsurprisingly the embedded Spotify player in ListenBrainz is now broken.

To reach feature-parity with the old player, we have to use the Web Playback API, which unsurprisingly seems to be designed to push developers towards registering their applications.

Is ListenBrainz a commercial project? Then we also need to get written approval from Spotify to use this.