Hi,
it is a while when I was playing with this idea within my own project (check this jIoT - home automatization).
I remember I was able to make it work but now when I tested it I’m not receiving any message in second device, even I’m successfully connected to Cayenne and subscribed to particular topic.
But you’re lucky, you can use already published REST API where you can query ALL sensors coupled with all devices.
I will try to play with MQTT topic in order to be sure I don’t have any mistake over there.
Y