var assistant = new watson.AssistantV1({
    username: '********',
    password: '******',
    url:'https://gateway.watsonplatform.net/assistant/api/v1 /workspaces/{workspaceid}  /message?version=2018-09-20',
    version: '2018-02-16'});

assistant.getIntent({
   intent: "Hello",
   workspace_id: '******'}, function(err, response){
   if(err){
      console.error(err);
   }else {
      console.log(JSON.stringify(response, null, 2));
   }
});

Error: Resource not found
code: 404,
error: 'Resource not found',
'x-global-transaction-id': 'ffea405d5c4ef5012b3fd98b'

url:'https://gateway.watsonplatform.net/assistant/api/v1/workspaces/{workspaceid}/message?version=2018-09-20'