Blueprint gives error in Automation (device_id)

Hey there!
I tried to write a blueprint that sends a push notification once the corresponding person comes home. However, I get the following error:

Logger: homeassistant.components.automation
Source: components/automation/__init__.py:280 
Integration: Automatisierung (documentation, issues) 
First occurred: 14:17:25 (1 occurrences) 
Last logged: 14:17:25

Blueprint Haustür Öffnen mittels Push Notification generated invalid automation with inputs OrderedDict([('tracker', 'device_tracker.iphone_von_felix'), ('notified_device', 'bbdbf897378ee59aca2d60f17ffa1135')]): required key not provided @ data['device_id']. Got None

The blueprint looks as such:

blueprint:
  name: Haustür Öffnen mittels Push Notification
  domain: automation
  input:
    tracker:
      name: Location Tracker
      description: Das Gerät (meist iPhone), dessen Position getrackt wird.
      selector:
        entity:
          domain: device_tracker
    notified_device:
      name: Notification Device
      description: Das iPhone, das die Push Notification erhält.
      selector:
        device:
          integration: mobile_app
trigger:
  - platform: device
    domain: device_tracker
    entity_id: !input tracker
    type: enters
    zone: zone.home
condition: []
action:
  - alias: Setup variables for the actions
    variables:
      action_open: "{{ 'OPEN_' ~ context.id }}"
  - alias: "Notify device"
    domain: mobile_app
    type: notify
    device_id: !input notified_device
    message: Haustür öffnen? (Long Press)
    data:
      actions:
        - action: "{{ action_open }}"
          title: Tür öffnen
          authenticationRequired: true
          icon: sfsymbols:lock.open
        - action: " {{ action_cancel }} "
          title: Abbrechen
          destructive: true
  - alias: "Wait for a response"
    wait_for_trigger:
      - platform: event
        event_type: mobile_app_notification_action
        event_data:
          action: "{{ action_open }}"
  - alias: "Perform the action"
    choose:
      - conditions: "{{ wait.trigger.event.data.action == action_open }}"
        sequence:
          - service: script.door_open
mode: single

Can anybody guide me to the error?