Simple automation looking for switch state change - help needed

I have just tried my first automation. I want to send an alert to my mobile when the front door bell rings. The door bell is connected to the input of a Shelly switch. The first version works well, but as expected, it triggers when the switch state changes from off to on, and then again from on to off. The Yaml is below, but I actually edited the automation in the configuration editor.

- id: '1636630015968'
  alias: Front Door Bell
  description: Alert on door bell
  trigger:
  - platform: state
    entity_id: switch.front_door_bell_switch_0
  condition: []
  action:
  - service: notify.mobile_app_s20fe
    data:
      title: Front door bell
      message: '{{states.switch.front_door_bell_switch_0.state}} at {{ now().strftime(''%H:%M:%S'')}}'
  mode: single

So I then added the ‘on’ state to the ‘to’ field of the trigger, which resulted in this

- id: '1636630015968'
  alias: Front Door Bell
  description: Alert on door bell
  trigger:
  - platform: state
    entity_id: switch.front_door_bell_switch_0
    to: 'On'
  condition: []
  action:
  - service: notify.mobile_app_s20fe
    data:
      title: Front door bell
      message: '{{states.switch.front_door_bell_switch_0.state}} at {{ now().strftime(''%H:%M:%S'')}}'
  mode: single

but now the automation does not trigger at all I have tried various combinations of typing the on state ie On “On”, ‘On’
In the first version the notification correctly displays the switch state as On then Off

Any suggestions how to correctly detect the On state?

Thanks

Use “Developer Tools / states” to take a look at the values while you are toggling the switch.

I think you need to use the value “on”.