app.registerPutHandler('vessels.self', 'navigation.racing.startLinePort', setStartLinePort) then what URL should I put to? /signalk/v2/api with the body {context :"", path : "vessles.self.navigation.racing.startLinePort", value : newPosition} ? OR is the plugin name and the path in the URI and the body is just the value? I've tried several combinations and can't work it out. Any pointers (or links to relevant documentation) greatly appreciated!