only a POST type is allowed. Running it from the browser is doing a GET. Try something like curl -i -X POST -d 'payload={"text": "Hello, this is some text."}' http://<mattermost-server-address>/hooks/zhr3si9q6jnbpy85ajgap7o3no
only a POST type is allowed. Running it from the browser is doing a GET. Try something like curl -i -X POST -d 'payload={"text": "Hello, this is some text."}' http://<mattermost-server-address>/hooks/zhr3si9q6jnbpy85ajgap7o3no