Zigbee2MQTT Thermostat - Howto "set" SetPoint (?)

Hi all,
i tried several ways but it seems there needs to be some more software engineering done than i think.

I have Sonoff ZigBee Thermostat-Heads that can be set remotely to a certain setpoint temperature.
I do receive the setpoint values if i change directly at the device. so the link is working.

Only to me its unclear how i can SET a setpoint from Openhab.

The Thing looks like this:
Type number : SonoffThermLR_setpoint "Sonoff ThermLR SetPoint [%.1f °C]" [ stateTopic="/z2m/Sonoff_ThermLR", transformationPattern="JSONPATH:$.occupied_heating_setpoint" ]

The Item as follows:
Number SonoffThermLR_setpoint "Sonoff ThermLR SetPoint [%.1f °C]" <radiator> (MyHeating) { channel="mqtt:topic:mosquitto:z2m:SonoffThermLR_setpoint"}

In rule and a switch item i tried the following, but it does not work and seems to not send anything back…

rule "Heater  TempSelect Switch"
    Item LRsel_Switch received command
    switch(receivedCommand) {
           case OFF : SonoffThermLR_setpoint.sendCommand(10)
           case ON : SonoffThermLR_setpoint.sendCommand(28)

PLEASE, highly appreciate your feedback on how to make this happen…

There is usually a command topic and a state topic.
ex. (From a UI generic zwave t0 Mqtt thing channel)

- id: Main_Floor_Heating_Setpoint_n
    channelTypeUID: mqtt:number
    label: Main Floor Heating Setpoint
    description: null
      commandTopic: zwave1/62/67/0/setpoint/1/set
      unit: °F
      min: 60
      formatBeforePublish: "%.0f"
      stateTopic: zwave1/62/67/0/setpoint/1
      max: 70

Thanks a lot for the “push”. i forgot that i have to use another commandTopic in the thing definition.
Plus the formatBeforePublish…not it works. THANKS