Amazon Polly configuration

Can anyone point me in the right direction to customize Amazon Polly to use the neural engine rather than standard? It doesn’t seem to matter what I put in in the configuration.yaml file for the voice and engine.

Here is my configuration.yaml:

tts:
  - platform: amazon_polly
    aws_access_key_id: !secret aws_access_key_id
    aws_secret_access_key: !secret aws_secret_access_key
    region_name: "us-west-2"
    text_type: ssml
    voice: Arthur
    cache: True
    engine: neural

Here is my script:

service: tts.amazon_polly_say
data:
  entity_id: media_player.bedroom_speaker
  message: |
    <speak><break time="1000ms"/>Hello this is a test 1 2 3 4 5 6 7</speak>