OpenHab, Shelly1, Mosquitto/REST - does not work

After reading this howto it is clearer now.

But after creating a Generic Thing and adding a new channel, the status is “OFFLINE - COMMUNICATION_ERROR java.lang.Exception: No MQTT client”

Perhaps there is a misconfiguration of the state and command topic:

stat/shellies/shelly1-15E1F2/relay/0/
cmnd/shellies/shelly1-15E1F2/relay/0/command

http://shelly-api-docs.shelly.cloud/#shelly1-overview:

Shelly1: MQTT
Shelly1 uses the following topics:

shellies/shelly1-<deviceid>/relay/0 to report status: on or off
shellies/shelly1-<deviceid>/relay/0/command accepts on and off and applies accordingly
Shelly1: /settings

That should be correct, isn’t it?