It don't support the module service-identity greater to 16.0.0. Fteproxy show this message:

:0: UserWarning: You do not have a working installation of the service_identity module: ' No module named x509'. Please install it from https://pypi.python.org/pypi/service_identity and make sure all of its dependencies are satisfied. Without the service_idetity module, Twisted can perform only rudimentary TLS client hostname verification. Many valid vertificate/hostname mappings may be rejected.

Suppose it's due to changes in cryptography.x509 in version 17.0.0 (It is the last one for now)

Temporary solution: pip install service-identity==16.0.0