It took me some time to figure out. So, maybe you want to add this to your website:
Shelly.call(
"HTTP.POST", {
"url": "http://localhost:8008/message?token=<apptoken>",
"content_type": "application/x-www-form-urlencoded",
"body": "message=<message>"
},
function(result) {
print(result);
}
);