zigbee2mqtt.yaml

mqtt:
  broker: homeassistant # This will have to be your mqtt broker
  discovery: true

input_boolean:
  zigbee_permit_join:
    name: Allow devices to join
    initial: off
    icon: mdi:cellphone-wireless

timer:
  zigbee_permit_join:
    name: Time remaining
    duration: 600

sensor:
  - platform: mqtt
    name: Bridge state
    state_topic: "zigbee2mqtt/bridge/state"
    icon: mdi:router-wireless

group:
  zigbee_group:
    name: Zigbee
    entities:
      - input_boolean.zigbee_permit_join
      - timer.zigbee_permit_join
      - sensor.bridge_state

automation:
  - id: enable_zigbee_join
    alias: Enable Zigbee joining
    hide_entity: true
    trigger:
      platform: state
      entity_id: input_boolean.zigbee_permit_join
      to: 'on'
    action:
    - service: mqtt.publish
      data:
        topic: zigbee2mqtt/bridge/config/permit_join
        payload: 'true'
    - service: timer.start
      data:
        entity_id: timer.zigbee_permit_join
  - id: disable_zigbee_join
    alias: Disable Zigbee joining
    trigger:
    - entity_id: input_boolean.zigbee_permit_join
      platform: state
      to: 'off'
    action:
    - data:
        payload: 'false'
        topic: zigbee2mqtt/bridge/config/permit_join
      service: mqtt.publish
    - data:
        entity_id: timer.zigbee_permit_join
      service: timer.cancel
    hide_entity: true
  - id: disable_zigbee_join_timer
    alias: Disable Zigbee joining by timer
    hide_entity: true
    trigger:
    - platform: event
      event_type: timer.finished
      event_data:
        entity_id: timer.zigbee_permit_join
    action:
    - service: mqtt.publish
      data:
        topic: zigbee2mqtt/bridge/config/permit_join
        payload: 'false'
    - service: input_boolean.turn_off
      data:
        entity_id: input_boolean.zigbee_permit_join

I got error messages like this to my home assistant log:
No matching payload found for entity: Bridge state with state_topic: zigbee2mqtt/bridge/state

Fixed it with this, maybe update your code?

• platform: mqtt
  name: Bridge state
  payload_on: "online"
  payload_off: “offline”
  state_topic: "zigbee2mqtt/bridge/state"
  icon: mdi:router-wireless

Is this your config for the sensor: component? That's also not working for me. Should it instead include:

payload_available: "online"
payload_not_available: “offline”

Hello Thanks for this file! :)
Where do I put this it?
I'm a bit lost!