I see the problem.
Unlike most Home Assistant media players - roon doesn’t assign unique ids to playlists etc.
So as a workaround I use a query path to identify the playlist.
You can see the documentation here:
RoonLabs music player - Home Assistant
An example from my library is
action: media_player.play_media
data:
media_content_type: music
media_content_id: Playlists/Alarm
target:
entity_id: media_player.bedroom
Please note the the roon API doesn’t currently let you play smart playlists.