Mosquitto broker setup

Configuration
1

I try to set up Mosquitto broker addon in Hassio.
But I get following error in the notifications.

image

What could be wrong?
My addon config looks like this:
image
And the configuration.yaml like this

mqtt:
  discovery: true
  discovery_prefix: homeassistant
2

I have this (default?) in the add-on config

logins: []
anonymous: false
customize:
  active: false
  folder: mosquitto
certfile: fullchain.pem
keyfile: privkey.pem
require_certificate: false

and no mqtt in configuration.yaml (and it works)