python urlopen错误以松弛状态发送消息

Question

import json
from urllib.request import Request, urlopen

SLACK_CHANNEL = '#alerts-sandbox'
SLACK_WEBHOOK_URL = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'

slack_message_alert = {'channel': SLACK_CHANNEL, "text": "The Schedule Environment is Automated to  environment."}
req_alert = Request(SLACK_WEBHOOK_URL, json.dumps(slack_message_alert).encode('utf-8'))
response_alert = urlopen(req_alert)
response_alert.read()

这是我的python 3.7代码，用于将消息发送到slack。 当我运行它时，出现此错误：

Traceback (most recent call last):
  File "C:/Users/payamzowghi/Desktop/scratches/scratch.py", line 674, in <module>
    response_alert = urlopen(req_alert)
  File "C:\Python37\lib\urllib\request.py", line 222, in urlopen
    return opener.open(url, data, timeout)
  File "C:\Python37\lib\urllib\request.py", line 531, in open
    response = meth(req, response)
  File "C:\Python37\lib\urllib\request.py", line 641, in http_response
    'http', request, response, code, msg, hdrs)
  File "C:\Python37\lib\urllib\request.py", line 569, in error
    return self._call_chain(*args)
  File "C:\Python37\lib\urllib\request.py", line 503, in _call_chain
    result = func(*args)
  File "C:\Python37\lib\urllib\request.py", line 649, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found

该代码在24小时前生效。我不知道为什么现在不起作用。请帮助我。