Having trouble with script playing a Sonos favourite to Sonos speaker group

All my speakers and entities appear in HA. I have set up a Sonos group for my downstairs speakers, the sonos integration is set up. I can play using the Sonos HACs card (which is great). But I’m trying to create an automation, but it will call a script. Script below should be working, but nothing happens. Can anyone see anything obvious? I’ve read through the documentation for media player and sonos. All my syntax seem OK.

As part of my question to those more experienced with Sonos, how do I get the Favorite’s media_content_id?

alias: Music_morning
sequence:
  - service: media_player.volume_set
    data_template:
      entity_id: media_player.sonos_downstairs
      volume_level: 0.4
  - service: media_player.play_media
    target:
      entity_id: media_player.sonos_downstairs
    data:
      media_content_type: favorite_item_id
      media_content_id: FV:2/1
mode: single

After some reading, tried this where Symphony_Hall is the name of a sonos favorite:
This also didn’t start playing.

alias: Music_morning
sequence:
  - service: media_player.volume_set
    data_template:
      entity_id: media_player.sonos_downstairs
      volume_level: 0.8
  - service: media_player.play_media
    target:
      entity_id: media_player.sonos_downstairs
    data:
      media_content_type: music
      media_content_id: Symphony_Hall
mode: single

So I’ve tried playlists and favorites in every which way, but no joy when I click “Run”.