How to play sound thru TCL/Roku TV

I have the Roku Integration installed and I can control my TVs; however, can someone walk me through how I can play a sound thru the TV as part of an automation? I created an automation which for purposes of testing is triggered on Time. The action looks like this:

action:
  - service: media_player.play_media
    target:
      device_id: 697ce11fbe7fc1c2a49556545689420245598f
    data:
      media_content_id: [a url pointing to an mp3]
      media_content_type: audio/mp3

Do I need additional actions to turn on the TV or change its state before playing the audio? This action works fine if the device_id points to my Google Home.

I see this in the log:

ERROR (MainThread) [homeassistant.components.roku.media_player] Invalid media type audio/mp3. Only app and channel are supported

I guess I can’t play a sound this way. Too bad. It would have been nice if I could use the TV as a speaker.

Maintainer of Roku integration here. What is the source of the audio? We can send some media types via recent updates using PlayOnRoku application that Roku provides for its mobile apps.

I can extend this to certain audio urls (looking into TTS first)