Sending error or log message via MQTT

I implemented a Node-RED flow which act like a Gateway for the Watson IoT Platform. I connected the Gateway via MQTT node to the IoT platform in order to send data for multiple sensor devices to the platform.

Now I would like to extend the gateway with error handling functionalities by sending the error message to the IoT platform. My goal is that the error messages appear then in the Diagnosis tab of the IoT platform.

I have searched for hours the web but couldn't find any informations about how I could send/publish error messages with MQTT. Is there a special topic I could use in order to setup an error message or is there no error sending functionality in MQTT at all?

I hope you can help me further. Thank you.

MQTT is just a message queue system so you can send it whatever you like - as long as it is as supported data type. String, Number, Boolean I think is about it.

Choose a suitable topic layout and use it.