Help w/ BluePrint

Trying to write a basic blueprint, my first one, but no idea what I"m doing wrong.
Did the following, but it doesn’t seem to replace the media_content_id correctly.
Any idea?

blueprint:
  name: Move Spotify Stream
  domain: script
  input:
    target_speaker:
      name: "Target Speaker"
      description: "Speaker to send stream to"
      default: []

mode: restart

sequence:
  - alias: "Send notification"
    service: media_player.play_media
    target:
      entity_id: media_player.main_bedroom    
    data:
      media_content_type: custom
      media_content_id: Play Spotify on !input target_speaker