How to setup a Sonoff 4ch in openHAB

[vzorglub (Vincent Regaud)]

First you need to use the code fences when publishing code:

How to use code fences

We all have to type this content over and over and over. Here is a posting we can all point to when the topic comes up. Why use code fences? Because rules, sitemap, logs, and configs are all but unreadable when code fences are not used. When to use code fences? Whenever one is posting any sort of code, config, log, and any text where line wrapping, indentation, and using an equal spaced font makes the text more legible. How to use code fences? Use 3 backticks (```)... Or use <code>... …

The answer to your problem is right under your nose:
The sonoff MQTT full topic is sonoff/cmnd/sonoff_MasterBedroom/

and topic used in your items is: sonoff/Sonoff4ch_4/cmnd/

Good luck