Hi, i was having the same issue today trying to chromecast to our Bang & Olufsen TV and im hoping my solution can help others on here struggling to get their Chromecast working.
Now, i assume that you already have google home installed on whichever device you used to setup your Chromecast. I dont believe it has to be on a certain device just as long as you have the app. If it IS NOT working currently and you already have google home installed then please follow these steps closely:
1. Make sure you uninstall the Google Home app, for me this is what was causing all the problems.
2. Reinstall the app
3. Open the app and wait for it to find your chromecast. MAKE SURE you are on the same wifi connection as your chromecast.
4. This should have fixed the issue, just close the Google Home app and re - launch Spotify.
5. Try chromecasting your music again by playing a song -> sellect devices -> chromecast.
With any luck its now working again! I hope this helped and it would be awesome if you could like this post if it worked for you. ✌