I only found it here: https://support.ptc.com/help/thingworx/platform/r9/en/index.html#page/ThingWorx/Help/Release_Notes/F... if you search for "MQTT Extension 3.1.0" in the page
I only found it here: https://support.ptc.com/help/thingworx/platform/r9/en/index.html#page/ThingWorx/Help/Release_Notes/F... if you search for "MQTT Extension 3.1.0" in the page