I wish I would have a crystall ball. As you probably notice novice level HA, so help is welcome. Log shows that stream is started, chromcast is switched on but nothing happens, it seems that the stream is not send properly (not sure how to check that). I’ve read more issues regarding that, but don’t know where to go from here
There’s a fairly recent issue relating to how spotify handles external requests for playlists. Lots of discussion about how the mopidy kids are dealing with it here: https://github.com/mopidy/mopidy-spotify/pull/188
Obviously, the fact that the pull above is for Mopidy, not HA, isn’t particularly helpful but the issue is the same - Spotify’s external access through libspotify is just not maintained and is probably being intentionally broken.
I imagine if you changed your json to request a track instead of a playlist (ie change the type to music and the id to a specific track) it would work fine…
When it comes to playing Spotify to Chromecast, if you meet Spotify to Chromecast not working issue, you can try another way to do it. Just use Spotify Downloader to download Spotify songs as local files and upload them to Google Play Music to mirror Spotify to Chromecast. Or just use Chrome to do it with ease.