In event that Fire UI is running on a different port, the configuration needs to be updated on Administration > Configuration > App > app.postMessageURL = Fire UI Custom Port else submission fails with the below error.
Sending 'POST' request to URL : http://localhost:8080/messageFromSparkJob
Response Code : 404
18/05/04 10:25:25 ERROR workflowengine.YARNRestWorkflowContext: http://localhost:8080/messageFromSparkJob
Probably this also needs to be updated here