The MQTT feature currently only supports publishing (i.e. for notification etc.), it does NOT support subscribing yet (i.e. receiving command). It’s quite easy to add support for subscription, but it hasn’t been done yet.
If you run a command using curl, you should put the command around “”, otherwise it will cut off at special characters like &. In fact, you should also use the -g option because characters like [ will also throw it off because it’s a globbing character. For example:
curl -g "https://demo.opensprinkler.com/mp?pid=0&uwt=0"
should work (note that the demo website is not password protected so I ignored the pw= parameters. Also note that the password needs to be a md5 checksum, so your ‘opendoor’ will not work. Instead, you should use the md5 checksum of opendoor, which is a6d82bced638de3def1e9bbb4983225c