ssl connection with certificate

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/index.html
Description:

Good morning. Following the instructions
https://www.postgresql.org/docs/11/ssl-tcp.html I can't establish a local
connection with certificate. In the pg_hba.conf 
hostssl    all             all             127.0.0.1/32            md5
clientcert=1

And in the postgresql.conf:

ssl_cert_file = '/etc/postgresql/11/main/server.crt'
ssl_key_file = '/etc/postgresql/11/main/server.key'

server is a certficate is generated.
The error all the time is the same, it cannot connect because either the
server is not activated or something is missing.

I need a possible solution. The installation I have done is the basic sudo
apt install postgresql on debian 10

Thanks and best regards,