Home Assistant Blueprint: Notify or do something when an appliance like a dishwasher or washing machine finishes

notify-or-do-something-when-an-appliance-like-a-dishwasher-or-washing-machine-finishes.yaml

blueprint:
  name: Appliance has finished
  description: Do something when an appliance (like a washing machine or dishwasher)
    has finished as detected by a power sensor.
  domain: automation
  input:
    power_sensor:
      name: Power Sensor
      description: Power sensor entity (e.g. from a smart plug device).
      selector:
        entity:
          domain: sensor
    starting_threshold:
      name: Starting power threshold
      description: Power threshold above which we assume the appliance has started.
      default: 5
      selector:
        number:
          min: 1.0
          max: 100.0
          unit_of_measurement: W
          mode: slider
          step: 1.0
    starting_hysteresis:
      name: Starting hysteresis
      description: Time duration the power measurement has to stay above the starting
        power threshold.
      default: 5
      selector:
        number:
          min: 0.25
          max: 60.0
          unit_of_measurement: min
          mode: slider
          step: 0.25
    finishing_threshold:
      name: Finishing power threshold
      description: Power threshold below which we assume the appliance has finished.
      default: 5
      selector:
        number:
          min: 1.0
          max: 100.0
          unit_of_measurement: W
          mode: slider
          step: 1.0
    finishing_hysteresis:
      name: Finishing hysteresis
      description: Time duration the power measurement has to stay below the finishing
        power threshold.
      default: 5
      selector:
        number:
          min: 0.25
          max: 60.0
          unit_of_measurement: min
          mode: slider
          step: 0.25
    actions:
      name: Actions
      description: Actions (e.g. pushing a notification, TTS announcement, ...)
      selector:
        action: {}
    pre_actions:
      name: Actions
      description: Actions when starting threshhold is crossed
      selector:
        action: {}
  source_url: https://gist.github.com/sbyx/6d8344d3575c9865657ac51915684696
trigger:
- platform: numeric_state
  entity_id: !input 'power_sensor'
  for:
    minutes: !input 'starting_hysteresis'
  above: !input 'starting_threshold'
condition: []
action:
- choose: []
  default: !input 'pre_actions'
- wait_for_trigger:
  - platform: numeric_state
    entity_id: !input 'power_sensor'
    below: !input 'finishing_threshold'
    for:
      minutes: !input 'finishing_hysteresis'
- choose: []
  default: !input 'actions'
mode: single
max_exceeded: silent

I was also struggling with the error message Message malformed: Missing input pre_actions.
You have to define a pre-action. If you do not need one, you can add just a 1s delay like @Steeveeveeve mentioned.
Here is my yaml file which you can copy and paste into the yaml editor.

alias: Waschmaschine ist fertig
description: ""
use_blueprint:
  path: >-
    sbyx/notify-or-do-something-when-an-appliance-like-a-dishwasher-or-washing-machine-finishes.yaml
  input:
    power_sensor: sensor.switch_bathroomfloor_plug_washingmashine_power
    starting_threshold: 100
    starting_hysteresis: 5
    finishing_threshold: 5
    finishing_hysteresis: 5
    actions:
      - service: notify.mobile_app_heliumhypernet
        metadata: {}
        data:
          message: Waschmaschine ist fertig
          title: I am done
    pre_actions:
      - delay:
          hours: 0
          minutes: 0
          seconds: 1
          milliseconds: 0