you need to use mqtt.mydevices.com server if you need to send data to cayenne. i made a test flow below which send data to cayenne. you need to add your MQTT credential in the flow.
[{"id":"b3eb01f7.3986d","type":"tab","label":"Flow 2","disabled":false,"info":""},{"id":"dbaacf13.048a3","type":"inject","z":"b3eb01f7.3986d","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":306,"y":162,"wires":[["9754bdfe.93395"]]},{"id":"9754bdfe.93395","type":"function","z":"b3eb01f7.3986d","name":"","func":"msg = {\n topic:\"v1/<username>/things/<slient_id>/data/1\",\n payload:\"temp,c=20\"\n};\n\nreturn msg;","outputs":1,"noerr":0,"x":543,"y":154,"wires":[["b0cd75dc.795b68"]]},{"id":"b0cd75dc.795b68","type":"mqtt out","z":"b3eb01f7.3986d","name":"","topic":"","qos":"2","retain":"","broker":"a30e1e3f.316ba","x":703,"y":174,"wires":[]},{"id":"a30e1e3f.316ba","type":"mqtt-broker","z":"","name":"cayenne","broker":"mqtt.mydevices.com","port":"1883","clientid":"<client_id>","usetls":false,"compatmode":true,"keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthPayload":"","closeTopic":"","closePayload":"","willTopic":"","willQos":"0","willPayload":""}]