OSError: [Errno 88] Socket operation on non-socket

Traceback (most recent call last):
  File "./fcgi.py", line 11, in <module>
    WSGIServer(app).run()
  File "/usr/local/lib/python3.8/site-packages/flup/server/fcgi.py", line 111, in run
    sock = self._setupSocket()
  File "/usr/local/lib/python3.8/site-packages/flup/server/fcgi_base.py", line 1025, in _setupSocket
    sock = socket.fromfd(FCGI_LISTENSOCK_FILENO, socket.AF_INET,
  File "/usr/lib64/python3.8/socket.py", line 544, in fromfd
    return socket(family, type, proto, nfd)
  File "/usr/lib64/python3.8/socket.py", line 231, in __init__
    _socket.socket.__init__(self, family, type, proto, fileno)
OSError: [Errno 88] Socket operation on non-socket