I was following the guide on building a control integration, up until https://devdocs.sonos.com/reference/playbacksession-loadcloudqueue-sessionid 
i have a audio playback focused webapp that wants to stream its content to sonos. i can successfully authenticate, discover and create a session. when i try to attach a playlist to the session using loadStreamUrl by specifying a queueBaseUrl to the groupId parameter i get a 501 error.
i implemented a set of endpoints on https://example.com/sonos/cloudQueue but i never see any requests hitting it.

interestingly, LoadAudioClip is working, but this is far from ideal.

sorry if this is not the ideal forum, i was not able to locate a “developers forum” otherwise.