Send data from ChirpStack to Home Assistant via MQTT

Most likely you are looking for:
https://www.chirpstack.io/docs/chirpstack/integrations/mqtt.html

The MQTT integration can be configured in the chirpstack.toml config file, example:

# Global integration related configuration.
[integration]

  # Enabled integrations (global).
  enabled = [
  ]

  # MQTT integration configuration.
  [integration.mqtt]

    # Event topic template.
    event_topic="application/{{application_id}}/device/{{dev_eui}}/event/{{event}}"

    # Command topic.
    #
    # This is the topic on which the MQTT subscribes for receiving (enqueue) commands.
    command_topic="application/{{application_id}}/device/{{dev_eui}}/command/{{command}}"

    # Use JSON encoding instead of Protobuf (binary).
    json=true

    # MQTT server (e.g. scheme://host:port where scheme is tcp, ssl or ws)
    server="tcp://127.0.0.1:1883/"

    # Connect with the given username (optional)
    username=""

    # Connect with the given password (optional)
    password=""

I've tried this configuration but it didn't work.

I created the file chirpstack.toml under the path /etc/chirpstack/ because it didn't exist there.

This is the payload I've added.

[integration]
  enabled = ["mqtt"]

  # MQTT integration configuration.
  [integration.mqtt]

    # Event topic template.
    event_topic="application/{{application_id}}/device/{{dev_eui}}/event/{{event}}"

    # Command topic.
    #
    # This is the topic on which the MQTT subscribes for receiving (enqueue) commands.
command_topic="application/{{application_id}}/device/{{dev_eui}}/command/{{command}}"

    # Use JSON encoding instead of Protobuf (binary).
    json=true

    # MQTT server (e.g. scheme://host:port where scheme is tcp, ssl or ws). The one running in Home Assistant.
    server="tcp://192.168.0.91:1883/"

    # Connect with the given username (optional)
    username="<redacted>"

    # Connect with the given password (optional)
    password="<redacted>"

I started 2 different MQTT Explorer:

1. One connected to MQTT Server running in ChirpStack; and
2. another one connected to MQTT Server running in HA.

I found the topic application in the MQTT Explorer connected to ChirpStack but nothing in the one connected to MQTT server running in HA.

My questions:

1. As far as I understood, those topics are really templates and I don't need to hardcode any application_id or dev_eui or ... there, right?
2. The IP should be the one of MQTT Server running in HA? Does the last slash ("/") matter?
3. Is there any specific log for this integration/communication? I've tried the system logs (Status > System Log from menu) but I couldn't find anything related to this integration (the IP configured) but just the logs related to the ChirpStack MQTT Forwarder.
4. Am I missing something?

Note: It's a bit tricky to debug this environment because the sensor transmit data every 12 hours. So, I'll need to wait a little bit until I validate this integration again.

Thanks in advance

Do you use a separate MQTT Broker for HA and for Chirpstack? If not, you can use the topics of Chirpstack in the configuration file of HA (configuration.yml):

mqtt:
  sensor:
    - name: "Water Meter Volume"
      unique_id: "water_meter_volume"
      state_topic: "application/<applicationid>/device/<deveui>/event/up"
      value_template: "{{ value_json.object.volume }}" <-- this is the volume key in the decoded MQTT JSON message)
      unit_of_measurement: "<check the correct unit>"
      device_class: <check the correct device_class>
      state_class: measurement

If you use two Brokers (one for HA and one for Chirpstack) you need to configure a bridge.

Here is an example:

connection bridge-from-ha-to-chirpstack
address <IP-Address to chirpstack broker>:8883

# Authentifizierung
remote_username USER
remote_password PW
# CLIENTID
clientid ha_bridge_to_chirpstack

# TLS 
bridge_capath /etc/ssl/certs/
bridge_insecure true

try_private false
notifications false
bridge_protocol_version mqttv311

topic application/<applicationid>/device/<deveui>/event/up/# in 0 ha/

If you use this configuration, you have to change the topic in the configuration.yml to ha/application/<applicationid>/device/<deveui>/event/up

The bridge.conf you need to put in \share\mosquitto folder of HA.

Which install did you do? If you did docker the chirpstack.toml file wouldn't be in /etc/chirpstack but /chirpstack-docker/configuration/chirpstack, I'd be surprised if you didn't already have the file and think you might be adding a file somewhere Chirpstack isn't looking.

You do not need to hardcode the values for dev-eui etc for the MQTT integation, those get filled appropriately.

I remember a bunch of people setting up Chirpstack with Home Assitant on the previous forum, searching doesn't seem to give many relevant results for some reason but I can personally remember at least 5 within the past two years. Here's an example: https://forum.chirpstack.io/t/working-example-homeassistant-to-lorawan-chirpstack-downlink-commands/24603