sudo systemctl start openvpn-server@server.service doesn't want to work

I have a problem with the OpenVPN service.

I've already changed the server.conf, sysctl.conf and before.rules settings,

specifically these changes,

tls-auth ta.key 0 # This file is secretcipher AES-256-CBCdh dh2048.pemnet.ipv4.ip_forward = 1

However, I cannot activate OpenVPN.

I'm following the step by step of this link,

https://www.digitalocean.com/community/tutorials/how-to-set-up-and-configure-an-openvpn-server-on-ubuntu-20-04-en

Here's the error:

● openvpn-server@server.service - OpenVPN service for server     Loaded: loaded (/lib/systemd/system/openvpn-server@.service; enabled; vendor >     Active: activating (auto-restart) (Result: exit-code) since Thu 2022-09-15 20>       Docs: man:openvpn(8)             https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage             https://community.openvpn.net/openvpn/wiki/HOWTO    Process: 90662 ExecStart=/usr/sbin/openvpn --status /run/openvpn-server/status>   Main PID: 90662 (code=exited, status=1/FAILURE)     Status: "Pre-connection initialization successful"        CPU: 21msSep 15 20:36:11 hydra systemd[1]: openvpn-server@server.service: Main process exit>Sep 15 20:36:11 hydra systemd[1]: openvpn-server@server.service: Failed with result>

Thanks to whoever responds.