Playing a Spotify playlist on a specific wha thing

I’d like to play a spotify playlist on a specific echo device or device group.

Since the spotify WebAPI only delivers 7 devices and the Ids are apperantly not stucked to a specific device, doing something like this produces different results:

spotifyDeviceId.sendCommand("02c10712-343a-4ce0-99dd-1bc9744119ec")

Sometimes the music is played in my kitchen, sometimes it’s played everywhere. It seems more or less random (there probably is some logic behind it).

I found a way to play a playlist on a specific echo device by doing the following:

Echo_kueche_MusicProviderId.sendCommand(SPOTIFY)
Echo_kueche_Player.sendCommand(PLAY)

spotifyPlaylists.sendCommand(spotify:playlist:+playlist)

This way music is always played in my kitchen.

I also have two echo devices grouped together (kitchen and bathroom) and would to start spotify on these devices simultaneously. So I added a WHA-Thing in my config. According to the Docs, WHA-Things do not support to write MusicProviderId (I tried it anyway…). But even using the player-channel does not work. I tried the following:

Echo_kuecheBadezimmer_Player.sendCommand(PLAY)

Also, when I use the spotify app to start playback on this group, the state delivered for this channel is still NULL

My Echo-Things:

Bridge amazonechocontrol:account:account1 "Amazon Account" @ "Accounts" [discoverSmartHome=2, pollingIntervalSmartHomeAlexa=10, pollingIntervalSmartSkills=60] {
    Thing echo			badezimmer			"Alexa Badezimmer" 			@ "Living Room" [serialNumber="..."]
	Thing wha			kuecheBadezimmer	"KuecheBadezimmer" 			@ "KuecheBadezimmer" [serialNumber="..."]
	Thing echo			kueche      		"Alexa Kueche" 				@ "Kueche" [serialNumber="..."]
}

My “KuecheBadezimmer”-Items:

Player Echo_kuecheBadezimmer_Player       		"Player"           		(Alexa_Studio) {channel="amazonechocontrol:echo:account1:kuecheBadezimmer:player"}
String Echo_kuecheBadezimmer_MusicProviderId    "Music Provider Id"     (Alexa_kueche) {channel="amazonechocontrol:echo:account1:kuecheBadezimmer:musicProviderId"}

Does anybody know how I can control the kuecheBadezimmer-Items?