Got message "Failed to execute asynchronous action" while running a DITA-OT Server output processing

Condition

The reported error is :

2020-03-17 20:24:41,621  ERROR [repo.action.AsynchronousActionExecutionQueueImpl] [defaultAsyncAction1] Failed to execute asynchronous action: Action[ id=82b81f6e-a3d0-4161-a652-5d2cb191e7e8, node=null ]
 com.componize.xml.pipeline.UserPipelineException: Connection refused (Connection refused)

And in the Java stack dump, there is a line like :

Caused by: org.springframework.web.client.ResourceAccessException: I/O error on POST request for "http://localhost:8090/jobs": Connection refused (Connection refused); nested exception is java.net.ConnectException: Connection refused (Connection refused)

Cause

The most common cause is that your DITA-OT Server is not running.

Remedy

Ask your administrator to start the DITA-OT Server.

Cause

You try to run a DITA-OT Server pipeline configuration (ex. ditaot-html5) but no DITA-OT Server is installed in your environment.

Remedy

Use Componize DITA-OT Pipelines instead (ex. map2html5 pipeline configuration).