send mqtt command versus device

[matc1]

Hi,  i configured an experiment with this network parameter

<connection address="MYSERVERIP:1883" autoConnect="true" interval="1" service="mqtt/json" receiveTopic="fancySensor/value" sendTopic="sensorlogger/data" id="test" privacy="https://phyphox.org/disclaimer/" conversion="json">
        <send id="x" type="buffer" datatype="number">accX</send>
        <send id="y" type="buffer" datatype="number">accY</send>
        <send id="z" type="buffer" datatype="number">accZ</send>
    </connection>

Is it possible via mqtt topic to send "start" and "stop" command to the device, like get command 

http://DEVICEIP:8080/control?cmd=start

http://DEVICEIP:8080/control?cmd=stop

I need to send data via receiveTopic?

My device is an Iphone

Is it possible to have an examples?

Thanks