I don't have this device, but when looking at the following documentation for MQTT (you gotta scroll down a bit), it looks like you need to publish a simple command to the appropriate topic
Topic:<topic_prefix>/command/switch:
Which I'm guessing is something like this for your case:
shellies/relay/command/switch:0
- or -
shellies/relay/ventilation/command/switch:0
Payload/Command (string): "on", "off", or "toggle"
Thanks, even though I have been through their documentation and tried all sorts of different setups, based on their info, but I probably don’t understand it.
Have you tried just using a tool like MQTT Explorer to publish values to the topics and get it working manually that way first? That would then get the topic and message figured out so you can program it then.
So Shelly's do MQTT out of the box? I was always tempted to get a Shelly Pro 4PM (ethernet-connected) but didn't take the leap because I try to minimize IP-based Home IOT devices vs using Z-Wave or Zigbee.
Yes, they do have MQTT out of the box. It works pretty well, and I had no problems getting it setup. Mine is actually in a IPX4 box outdoors and still managed to hold up through the summer.
Getting my Shelly HT modules up and running, creating UDT's for reference tags didn't take long.
I'm planning to let my ignition maker take over the home automation.
Next project will be able to handle the load balancing on our charging points where I live approx 5-6 charges where I might use one of Shellies to measure current power consumption and then determine what is left for charging points and thereby set the limit on them. But that is the day after tomorrow problem