Hi Arkesh
If you simply want to post a sample message to PI, you dont have to worry about Message Listner.
Simply Create a New Transaction in MII work Bench with HTTP post action Block, see below.
Next, Open the configuration links and set up your URL for PI, Content Type as text/xml if you are posting XML message and set up credentials in username and password, see below.
Save and Run your transaction. Hope this helps.