Error installing SSL from Let's Encrypt?

Question

CentOS

I'm trying to install ssl from Let's Encrypt according to the instructions - https://almostover.ru/2017-04/get-letsencrypt-free... I execute
the command:

certbot-auto certonly --allow-subset-of-names --agree-tos -m [email protected] --rsa-key-size 4096 --standalone --preferred-challenges http --http-01-port 9999 --server https://acme-v01.api.letsencrypt.org/directory -d site.ru

and an error is thrown:

[[email protected] ~]# certbot-auto certonly --allow-subset-of-names --agree-tos -m [email protected] --rsa-key-size 4096 --standalone --preferred-challenges http - -http-01-port 9999 --server https://acme-v01.api.letsencrypt.org/directory -d site.ru
/root/.local/share/letsencrypt/lib/python2.6/site-packages/ cryptography/__init__.py:26: DeprecationWarning: Python 2.6 is no longer supported by the Python core team, please upgrade your Python. A future version of cryptography will drop support for Python 2.6
DeprecationWarning
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Obtaining a new certificate
/root/.local/share/letsencrypt/lib/python2.6/site-packages/acme/jose/jwa.py:110: DeprecationWarning: signer and verifier have been deprecated. Please use sign and verify instead.
signer = key.signer(self.padding, self.hash)
Performing the following challenges:
http-01 challenge for site.ru
Waiting for verification...
Challenge failed for domain site.ru
Cleaning up challenges
Challenges failed for all domains

What's the matter?