Control Spotify Connect with a MEDION web radio

Hi Team,
I have a Medion web radio that integrates via Frontier Silicon integration.
Its working well from the UI and I can select the different sources.

However, when I am trying to send a Spotify playlist to the radio I get an error message:

Logger: homeassistant.components.frontier_silicon.media_player
Source: components/frontier_silicon/media_player.py:292
Integration: Frontier Silicon ([documentation](https://www.home-assistant.io/integrations/frontier_silicon), [issues](https://github.com/home-assistant/core/issues?q=is%3Aissue+is%3Aopen+label%3A%22integration%3A+frontier_silicon%22))
First occurred: 16:09:19 (1 occurrences)
Last logged: 16:09:19

Got playlist, but frontier_silicon only supports playing channels

Here is the automation I use:

action:
  - service: media_player.select_source
    data:
      source: "Spotify"
    target:
      entity_id: media_player.elternbad2
  - service: media_player.play_media
    target:
      entity_id: media_player.elternbad2
    data:
      media_content_id: "https://open.spotify.com/playlist/37i9dQZEVXcOXEoFU52cT7"
      media_content_type: playlist

Can anyone please help me how to get this to work?
Thanks,
Matthias