Just an FYI - Shelly dimmers - they work great with DemoPad with their native firmware. Simple http (port 80) commands, with feedback.
Use } as response terminator in feedback section.
Command examples:
On: GET /light/0?turn=on HTTP/1.0\x0D\x0A
Off: GET /light/0?turn=off HTTP/1.0\x0D\x0A
Toggle: GET /light/0?turn=toggle HTTP/1.0\x0D\x0A
Brightness 5%: GET /light/0?brightness=05 HTTP/1.0\x0D\x0A
Brightness 10%: GET /light/0?brightness=10 HTTP/1.0\x0D\x0A
Brightness 80%: GET /light/0?brightness=80 HTTP/1.0\x0D\x0A
Feedback for on: "ison":true
Feedback for off: "ison":false
Feedback for brightness level: "brightness":100