HTML5 Push Notification target help

I have just set up push notifications and they work fine when sending to all devices. e.g

  - service: notify.notify
    data:
      message: "A light has turned on"
      title: "Light On"    

However if I try to specify my (or my gf’s) android phone as the target then the notification doesn’t come through. e.g.

  - service: notify.notify
    data:
      message: "A light has turned on"
      title: "Light On"    
      target: "unnamed device_2"

If I specify my laptop as the target then it does work.
Anyone know why this is happening / is there a fix?

Thanks

below works. just verified
maybe use single quote not double?

- alias: 'Notify Gate Closed'
  trigger:
    - platform: state
      entity_id: binary_sensor.entry_gate
      from: 'on'
      to: 'off'
  action:
    - service: notify.notify
      data:
        title: 'GATE'
        message: 'Closed'
        target:
          - 'only_my_phone'
        data:
          tag: alert
          url: 'https://my_HAserver.com'
          image: "https://my_HAserver.com/api/camera_proxy/camera.mycamera?api_password=MyHAPassword"
          vibrate:
            - 300
            - 100
            - 400
          renotify: 0
          timestamp: '%m%d%H%M%S'