I can’t control my Chromecast using Spotify in beta
Spotify premium account is mandatory.
Some player like Google home cannot be discovered by the Spotify API. To make it works on the Smart Remote, you need to start playing your song with an official Spotify app first.
The Smart Remote doesn't support Chromecast out of the box. So to control Spotify running on Chromecast you need to:
Launch Spotify with the application (the mobile app, the web application, the Mac application or the Windows application)
Cast the application it on the Chromecast
You can now interact with Spotify interface on your Smart Remote with Spotify playing on your Chromecast.
Unlike Amazon's Echo devices, a Chromecast player is on the application that launched Spotify. It must, therefore, remain open.
See Spotify Chromecast supported devices here:
Google Chromecast Audio
Google Chromecast Ultra