YAML: Use device.state.MediaState in a script gives an error

[JacobWaterweg]

condition:
  type: device.state.MediaState
  device: My Device - Room Name
  state: playbackState
  is: PLAYING 

I want to use the above condition for my Nest Audio Speaker, as is indicated in the examples.  
Validating the script gives the message that: device.state.MediaState is not supported for this device.

Do I do something wrong or is there another way to check if the Nest Audio Speaker is active playing music?

[keyvez]

Same error for a speaker, if mediastate isn't going to work on a speaker when is it meant for something else like a TV?

[munnk82]

same error. neither nest speakers, nor chromecast audio works.

[berdan]

Same error for me too :
[is_playing] isn’t a valid state field for [MediaStateState]. The list of supported field paths: [playbackState].
starters:
type: device.state.MediaState
device: Kitchen pair - Kitchen
state: isPlaying
is: true