If it fails at step 3 with error 400, it probably means that Intalio|BPMS runtime is not up and running or it is configured differently than default. To check this out, you can try to go to
http://localhost:8080/wds/ in your web browser. If this gives you an error page, then it confirms that either Intalio|BPMS runtime is not running (it must be up and running if you want to register your task), or it is deployed with a different configuration (either remotely or on a different port), in which case you have to change localhost:8080 with your configuration, and you need to provide this at step 3.
If
http://localhost:8080/wds shows a white page with the text "Intalio|BPMS Workflow Deployment Service ", then it means Intalio|BPMS runtime is up and runnning with default configuration, and step 3 should not return this error message.
Please check this out and let us know.