Automation to publish and update notification on secondary MQTT trigger (frigate)

Thanks for offering to take a look.
In TheFes’s global variable topic, it was identified that the errors didn’t match my assertion!
I’ve fixed the real issue in the code below, it is all working.

My issue all along was that I wrapped the variable in double curlies, inside an expression.

  - alias: "Security: Object Detected"
    id: "HD2f4Q5RbLgXv"
    mode: parallel
    triggers:
      - trigger: mqtt
        alias: "topic published to /reviews"
        topic: "frigate/reviews"
        id: frigate-event
        payload: "alert"
        value_template: "{{ value_json['after']['severity'] }}"
    variables:
      type: "{{ trigger.payload_json['type'] }}"
      review_id: "{{ trigger.payload_json['after']['id'] }}"
      camera: "{{ trigger.payload_json['after']['camera'] }}"
      before_zones: "{{ trigger.payload_json['before']['data']['zones'] }}"
      after_zones: "{{ trigger.payload_json['after']['data']['zones'] }}"
      before_objects: "{{ trigger.payload_json['before']['data']['objects'] }}"
      after_objects: "{{ trigger.payload_json['after']['data']['objects'] }}"
      sub_labels: "{{ trigger.payload_json['after']['data']['sub_labels'] }}"
      detections: "{{ trigger.payload_json['after']['data']['detections'] }}"
      thumbnail: "https://ha.mydomain.com/api/frigate/notifications/{{detections[0]}}/thumbnail.jpg"
      snapshot: "https://ha.mydomain.com/api/frigate/notifications/{{detections[0]}}/snapshot.jpg"
      clip: "https://ha.mydomain.com/api/frigate/notifications/{{detections[0]}}/clip.mp4"
      msg_description: "{{ after_objects|join(', ')|title }} detected"
      msg_title: "{{ camera|title }} camera event"
    actions:
      - parallel:
          - sequence:
              - condition: template
                alias: Object lifecycle has ended
                value_template: '{{ type == "new" }}'
              - wait_for_trigger:
                  - trigger: mqtt
                    topic: frigate/tracked_object_update
                    value_template: '{{ value_json["type"] == "description" and value_json["id"] in detections }}'
                timeout:
                  seconds: "120"
              - condition: template
                alias: Object updated
                value_template: "{{ wait.completed }}"
              - event: set_variable
                event_data:
                  key: "{{ review_id }}"
                  value: "{{ wait.trigger.payload_json['description'] }}"
                  set_timestamp: false
          - sequence:
              - action: notify.residents
                data:
                  title: "{{ msg_title }}"
                  message: "{{ msg_description }}"
                  data:
                    subtitle: "{{ state_attr('sensor.variables', 'variables')[review_id] }}"
                    subject: "{{ state_attr('sensor.variables', 'variables')[review_id] }}"
                    group: "Security"
                    channel: "MEDIUM"
                    image: "{{ thumbnail }}"
                    tag: "{{ review_id }}"
                    entity_id: camera.{{ camera }}
                    color: "#FFFF00" # YELLOW
                    ledColor: "#FFFF00" # YELLOW
                    importance: high
                    priority: "high"
                    ttl: 0
                    persistent: "false"
                    sticky: "false"
                    actions:
                      - action: "URI"
                        title: "Thumbnail"
                        uri: "{{ thumbnail }}"
                      - action: "URI"
                        title: "Image"
                        uri: "{{ snapshot }}"
                      - action: "URI"
                        title: "Video"
                        uri: "{{ clip }}"
              - condition: template
                alias: Object lifecycle has ended
                value_template: '{{ type == "end" }}'
              - event: remove_variable
                event_data:
                  key: "{{ review_id }}"