Unable to upload file in chat using API and postman

Question

My goal is to upload the file from my custom widget, whenever agent request for fill upload.

When agent request file upload from salesforce chat, I am trying to upload file from postman by hitting Endpoint uploadServletUrl

Whenever any agent request to upload a file, I am receiving following event:

{
  "messages": [
    {
      "type": "FileTransfer",
      "message": {
        "uploadServletUrl": "https://myorg-url-.develop.my.salesforce.com/services/liveagent/file",
        "fileToken": "L-28bbffad-0544-4dcc-b459-f29b4c307bfb",
        "cdmServletUrl": "https://myorg-url-.develop.my.salesforce.com/liveagent/chatwindowfiletransfer.jsp",
        "type": "Requested"
      }
    }
  ],
  "sequence": 4,
  "offset": 2215002625
}

Now when ever I'm hitting uploadServletUrl from postman as following:

Body as

I'm getting 200 Status code, But Failure Message.

and in salesforce

For the info: Things are working fine, when I'm using Salesforce Livechat widget.