How activate Speaker Groups in the Yamaha MusicCast Integration

Hey,

I’m searching for a “How to” use the Group Funktionality from the Musiccast Integration.

With the HACS Frontend “Mini Media Player” i build up my media card:

The Devices are shown up, but when i try to aktivate the second speaker “Küche” i just get:
“Fehler beim Aufrufen des Diensts musiccast_yamaha/join. Service not found.”

type: entities
entities:
  - type: custom:mini-media-player
    group: true
    name: Wohnzimmer
    toggle_power: false
    artwork: cover
    hide:
      icon: true
      power_state: false
    speaker_group:
      platform: musiccast_yamaha
      expanded: true
      entities:
        - entity_id: media_player.wohnzimmer
          name: Wohnzimmer
        - entity_id: media_player.kuche
          name: Küche
    entity: media_player.wohnzimmer

I do not find any solution, to easy aktivate a speaker group.
Can you help me out?

BG