Here's a snippet of code that works. I use it for versioning the MC-110/120 modules. This way I can see in the ide which ones have the latest code.
Class mqtt_json
Shared version As Float
Shared Event Boot()
'############ This is your mcMod software version. You can see the version in the first byte of beacon data in Device maintenence and Connections under the ->Tools->Devices menu.
version = 2
'############ Add the version to the first byte of beacon data.
Dim beacondata As ListOfByte = New ListOfByte()
beacondata.Add(version.ToByte)
Lplan.SetBeaconData(beacondata)
'### Write out boot acknowledgement for debugging. Not required for the beacon, but picked up in an MQTT subscription
Dim id As String = Device.mcUID().ToString("x8")
Lplan.Publish("mqtt/boot", ("{Boot:" + id + ",Version:" + version.ToString+ "}").ToListOfByte, QoS.AtLeastOnce)
End Event