Trying to upload a .zip file to Playfab using Python - Get 10054 Error from server

I'm very new to Python and Web programming. I was given a task to upload new server builds to Playfab automatically - as my very first introductory task to Web programming.

My Question:

After getting an upload url from Play fab I'm trying to send it a .zip file with server build. But for some reason I'd always get 10054 Error

After looking at given documentation on how to upload custom server from Playfab I just cannot understand why I get kicked from server.

Here is the code that I'm using to upload:

def UploadZipFile(url_):
with open('D:/Bla/Bla/Bla/Server/TestServer.zip', 'rb') as _file:
    # If we got URL
    if url_ is not None:

        _header = {
            "Content-Type": "application/x-zip-compressed",
            "X-SecretKey": "TheKey"
        }
        _uploadRequest = requests.post(url_, data=_file, headers=_header)
        print _uploadRequest
        if _uploadRequest.status_code is not 200:
            print 'Could not upload file to server, response code {0}'.format(_uploadRequest.status_code)
            return False
        else:
            print 'Uploading files to server'
            return True
    else:
        print 'Got bad Upload URL'
        return False

This is very much a test code that I use. Not going into production.

To POST requests I'm using Requests Library

Thank you very much.