WebSocket can only connect server with machine name but not with actual IP address

There is no errors when I use machine name to connect, The code is paste below:

ws_address = "ws://{}:{}/WebSocket".format("hostname", 15000)

print("Connecting to WebSocket " + ws_address + " ...")

web_socket_app = websocket.WebSocketApp(ws_address, header=['User-Agent: Python'],
on_message=on_message,
on_error=on_error,
on_close=on_close,
subprotocols=['tr_json2'])

web_socket_app.on_open = on_open

wst = threading.Thread(target=web_socket_app.run_forever)

wst.start()

When I change "hostname" to the actual IP of the same host, it complains on:

[WinError 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

Please advise, thanks!