I can’t get tts.speak to work

Hi all!
I can’t get tts.speak to work! I’m testing with wyoming and piper, default configuration.
My test service call is:

service: tts.speak
data:
  cache: true 
  message: is it raining?
  media_player_entity_id: media_player.stua
target:
  entity_id: tts.piper

Not a sound can be heard.
My media players are Sonos speakers.
The piper debug log says:

DEBUG:wyoming_piper.handler:Sent info
DEBUG:wyoming_piper.handler:Sent info
DEBUG:wyoming_piper.handler:Synthesize(text='Is it raining?', voice=SynthesizeVoice(name='en_US-kathleen-low', language=None, speaker=None))
DEBUG:wyoming_piper.handler:synthesize: raw_text=Is it raining?, text='Is it raining?'
DEBUG:wyoming_piper.handler:input: {'text': 'Is it raining?'}
DEBUG:wyoming_piper.handler:/tmp/tmp5ow2l6r8/1695039829057415081.wav
DEBUG:wyoming_piper.handler:Completed request
DEBUG:wyoming_piper.handler:Sent info

I have tried clear_cache as well as different languages/voices.
I must be making some silly mistake here?
I’m running version 2023.9.2, operating system 10.5 on an Intel NUC

Please help. What is my silly mistake?