Web audio works, Chrome cast audios don't

I have several chrome cast audios through my house so they would be ideal for the text to speech stuff in openhab 2, but they just don’t work!

If I select web audio as the default sink then it works great, but selecting any of the chromecasts just doesn’t produce any sound.

I can hear the chromecast kick in (also it will stop anything else playing) so I can tell it’s trying to send audio, but none comes out.

Any ideas?

Is there any sort of logging I can add. I’m not seeing anything either way.

Does anyone have this working? It’s driving me nuts as it could be such a cool feature!

I had to set the callback URL of the Chromecast binding to equal the IP and port of the openhab instance and all seemed to work. Is this set?