Hi, This would not work from IOT devices supporting only http get webhooks because those devices simply make a http GET request - however they don’t process the HTML received as the response. They don’t have browsers to do that 
Your solution probably works only when you use your browser to fire the mentioned
openhab:8080/basicui/CMD?item=command
link.
You can simulate http GET to check it in a way any devices would with a tool called curl or wget, etc.
Please check the bidning proposal here - [webhook] New, very simple binding for listening incomming http requests . This can be used with http-get-only webhook devices.