Hello,
I have added a response on another (related) thread : Arduino UNO WiFi to cayenne dash board - #25 by adam. I am now using the PubSubClient MQTT library from Nick O’Leary (available on Github). It succesfully attempts an MQTT session with the Cayenne MQTT Server, but the Server rejects the Arduino (RC = -2). Details on the other thread.
Thanks for any help