Please format your code block so we tell if that is the source of the problem.
One glaring issue is that you have not provided a delay. Without a delay, the service calls will be made immediately one after the other. That means one of more of the calls will reach Amazon’s servers while the sound is already playing, which can cause the request to be dropped on their side. Your delay should be about as long as the play length of the sound, and having it a little longer is better.
FWIW, the best you’re likely to get is kind-of-simultaneous… playing sounds doesn’t seem to work on Alexa speaker groups, so you have to call the service on multiple targets, but they rarely play at the exact same time…
- repeat:
count: 5
sequence:
- service: media_player.play_media
data:
media_content_id: amzn_sfx_doorbell_chime_01
media_content_type: sound
target:
entity_id:
- media_player.living
- media_player.kitchen
- delay: 2