Are you reading the right post
example
[{"id":"f6ee0c7b.18c73","type":"inject","z":"d1395164b4eec73e","name":"on","props":[{"p":"topic","vt":"str"},{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"add_your_shelly_id_here/rpc","payload":"{\"id\":123,\"src\":\"any_string_you_wish\",\"method\":\"Switch.Set\",\"params\":{\"id\":0,\"on\":true}}","payloadType":"json","x":270,"y":4760,"wires":[["5e2a3763d28e983c"]]},{"id":"5e2a3763d28e983c","type":"mqtt out","z":"d1395164b4eec73e","name":"","topic":"","qos":"","retain":"","respTopic":"","contentType":"","userProps":"","correl":"","expiry":"","broker":"e8ba3ef5.22f4a8","x":410,"y":4760,"wires":[]},{"id":"e8ba3ef5.22f4a8","type":"mqtt-broker","name":"testb","broker":"192.168.1.25","port":"1883","clientid":"","autoConnect":true,"usetls":false,"compatmode":false,"protocolVersion":"4","keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthRetain":"false","birthPayload":"","birthMsg":{},"closeTopic":"","closeQos":"0","closePayload":"","closeMsg":{},"willTopic":"","willQos":"0","willPayload":"","willMsg":{},"userProps":"","sessionExpiry":""}]
add you shelly device id to the topic where it says add_your_shelly_id_here
