Problem with automation I thought was working

I’ve got a very simple automation that turns a light on or off when a switch in Smartthings is on or off.
I know my MQTT setup is working. I can see the switch position in Smartthings matches the switch position in the web UI. This works intermittently, only sometimes turning the light on. I’ve stared at this so long, I’m sure I’m missing something.

My code is:

- id: '13'
  alias: Hallway Switch
  - entity_id: switch.hallway_switch
    platform: state
    to: 'on'
  - entity_id: switch.hallway_switch
    platform: state
    to: 'off'
  - platform: mqtt
    payload: 'on'
    topic: "smartthings/Hallway Switch/switch"
    entity_id: light.hallway
    service_template: >
      {% if trigger.payload == 'on' %} 
      {%- else -%}
      {% endif %}

The main problem you have is that if the automation is triggered by the hallway switch you wont have a trigger payload for the template.