Cannot get Home Assistant to show devices from Homey using an MQTT Broker

I did the following to get my Athom Homey devices in home assistant:

  1. Install and configure Home Assistant on Synology NAS in Docker (package)
  2. Install and configure a Mosquitto broker (package) on Synology NAS
  3. Install MQTT client app on Homey and configure it to connect to the broker
  4. Install MQTT Hub app on Homey and configure it for Home Assistant discovery
  5. Set up an integration to the broker in Home Assistant configuration

In my opinion step 1 till 4 are successfull, but step 5 is not successfull.
In Step 5 I added the MQTT integration in Home Assistant and connected it with the correct IP-adress, port number 1883 and the correct username and password.

When I look into MQTT Explorer, there is nothing shown at homeassistant
What am I doing wrong? There are no entries in my logging.