OH3 with MQTT

I have a beginners understanding problem:
Setup on a raspberry pi OH3 and MQTT. Everything works fine in a terminal eg:
mosquitto_pub -h “MyIP” -p “MyPort” -t “myTopic” -m {on | off } -u “uname” -P “pwd”
Switch is turned on and off.
In OH3
Installed the binding
Created a MQTT Bridge. Added uname and pwd in the configuration
Created a Thing Generic MQTT Thing
Add a channel
MQTT Command Topic: “myTopic”
Custom On/Open Value: on
Custom Off/Closed Value: off
Add in a page a switch
Configured widget: With the item created.
Test the switch in the page: Nothing happens.
openhab-cli showlogs:
MqttSwitch01_MqttSwitchChannel01’ received command OFF or ON

What do I miss here?
Thanks for a feedback.

You don’t describe how you created the Item. Is the Item linked to the Channel?

Show the Thing config. Click on the code tab and post that here. Use code fences:

code goes here

Verify that the Things are ONLINE.

Use an MQTT client like MQTTExplorer to watch the messages as they are published (if they are published).

Thing Code looks like this:

label: MqttShellySwitch
thingTypeUID: mqtt:topic
configuration: {}
bridgeUID: mqtt:broker:MqttBroker
  - id: MqttShellySwitchChannel0
    channelTypeUID: mqtt:switch
    label: MqttShellySwitchChannel0
    description: ""
      commandTopic: shellies/shellyswitchXXXXXXX/relay/0/command
      postCommand: false
      retained: false
      qos: 0
      off: off
      on: on

Things are always Online
But the link I created was invalid.
Dropped and recreated the link. Specified the corresponding item.
Now it works.
Thanks for your feedback.