Add button to auto-discovered mqtt device

Hello,
I have tablet with the WallPanel-App running on it.
I enabled MQTT and successfully get the sensors from this device.


Since the controll commands are not exposed, I want to add them manually to the device, for example, reload:

mqtt:
  - button:
      name: "Reload"
      unique_id: "WallPanelEG_reload"
      availability_topic: "wallpanel/mywallpanel/connection"
      device:
        identifiers:
          [WallPanelEG", Google", "Fire", "9d64558e4b8da9bff52382ef399dc29c"]
        configuration_url: "homeassistant://config/devices/device/9d64558e4b8da9bff52382ef399dc29c"
        name: "WallPanelEG"
        manufacturer: "Google"
        model: "Fire"
      command_topic: "wallpanel/mywallpanel/command"
      payload_press: '{"reload": true}'

The button is created and works, but HA always creates a new device for it. I can’t get it to add id to the existing discovered device…



Can someone tell me what my mistake is?