输入以下命令，报错，是什么原因啊 ？

(python_mall) [root@VM-8-15-centos https]# python acme_tiny.py --account-key ./account.key --csr ./domain.csr --acme-dir /home/challenges/ > ./signed.crt

Parsing account key...

Parsing CSR...

Found domains: 81.71.93.230

Getting directory...

Directory found!

Registering account...

Already registered!

Creating new order...

Traceback (most recent call last):

  File "acme_tiny.py", line 198, in <module>

    main(sys.argv[1:])

  File "acme_tiny.py", line 194, in main

    signed_crt = get_crt(args.account_key, args.csr, args.acme_dir, log=LOGGER, CA=args.ca, disable_check=args.disable_check, directory_url=args.directory_url, contact=args.contact)

  File "acme_tiny.py", line 121, in get_crt

    order, _, order_headers = _send_signed_request(directory['newOrder'], order_payload, "Error creating new order")

  File "acme_tiny.py", line 60, in _send_signed_request

    return _do_request(url, data=data.encode('utf8'), err_msg=err_msg, depth=depth)

  File "acme_tiny.py", line 46, in _do_request

    raise ValueError("{0}:\nUrl: {1}\nData: {2}\nResponse Code: {3}\nResponse: {4}".format(err_msg, url, data, code, resp_data))

ValueError: Error creating new order:

Url: https://acme-v02.api.letsencrypt.org/acme/new-order

Data: b'{"protected": "eyJ1cmwiOiAiaHR0cHM6Ly9hY21lLXYwMi5hcGkubGV0c2VuY3J5cHQub3JnL2FjbWUvbmV3LW9yZGVyIiwgImFsZyI6ICJSUzI1NiIsICJub25jZSI6ICIwMDA0bXJiOEE3Z2c2cGhfU0pKT0FEamJjTncyVU80VkpXNlJDOGJwMU9LcTJMZyIsICJraWQiOiAiaHR0cHM6Ly9hY21lLXYwMi5hcGkubGV0c2VuY3J5cHQub3JnL2FjbWUvYWNjdC8xMjQyMjU2OTgifQ", "payload": "eyJpZGVudGlmaWVycyI6IFt7InR5cGUiOiAiZG5zIiwgInZhbHVlIjogIjgxLjcxLjkzLjIzMCJ9XX0", "signature": "fW42H78JHuuLn30fwXaZUZkrL-4BbZhZRHUgcbNeGVHpewEo7_nH3hTCqwtn3IsUU802lV45w1dX_mjEw_okYcIHTWGgwuz0ydBrKzyXThsKsI29ZyNqnVktLfuUYXe-eI3dII7PXKzvDs3zHLEAAIhHxhAVd5bQV-BtKNLaHmuhnzt_W3Fh6z8DMTCY3Z4S9zKgjYx7U-yP4DTbPEZTMo62gPPB6oUco36pocAxqS-95e6bebAMm9Yv-ct0H8E9xsR3nHju3Dmw1Do10hUMcoBUQGf0jiJsXFwJivhEPsCIfEAd7OaILh3yL_2ogRBH1IK2jjh3_qyWSKDswfiw-8pdauKGRjx3BLx9gOA7_LaI4SLUjxOCsLc96UASgRdcEy3YJF4M_z7pdkyFwE56n0zaT0vH5AmRzj3dmr8rrbp8CFQKP7CbJ7RUv42-37GcqkmvyyWS4o9VKJjR4rRA6xmcBvhltAjvM-Vszl99nZe2or8wBAWGXTQToSx3o0db92SPj3rKDdTKplWaDzRVeqTxiYnbjoAEy1VgzKB1trDoRtVor5ZXybkn5U9v6vGyY2jwAb80CnVQEX3z7s1fVxZx0VlwxJQCz0eduszKcbOjE8fO372epFiNEUfh_uVsXr_pMNka7O8KweKhDI-BvrmsJWD1LbqGqFoORNrQEaM"}'

Response Code: 400

Response: {'type': 'urn:ietf:params:acme:error:rejectedIdentifier', 'detail': 'Error creating new order :: Cannot issue for "81.71.93.230": The ACME server can not issue a certificate for an IP address', 'status': 400}