Ha-sip and Piper: Outgoing call is working, but text is not spoken

Hi all,

when I’m running the action

action: tts.speak
metadata: {}
target:
  entity_id: tts.piper
data:
  cache: true
  media_player_entity_id: media_player.browser_mod_5def8a21_5770b36b
  message: Testnachricht

the call is working, but the text is not spoken.

If I run the action

action: hassio.addon_stdin
data:
  addon: c7744bff_ha-sip
  input:
    command: dial
    number: sip:[email protected]
    ring_timeout: 20
    menu:
      message: Hallo, das ist eine Nachricht von Home Assistant.
      wait_for_audio_to_finish: true 
      post_action: hangup

the text is spoken.

Any suggestion how to get piper to speak the text in a call?

Thx

.g