SSL for a VPS not working

Hello,
I have a VPS in address server.domain.gr and the Let’s Encrypt SSL certificate for the server (server.domain.gr) has expired but not for the domain.gr
I use Cloudflare for the domain but not for the server and while trying to renew the certificate i get the following error.
Any help please ??


Requesting a certificate for server.domain.gr from Let’s Encrypt …
… request failed : Web-based validation failed :
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for server.domain.gr
Using the webroot path /home/domain/public_html for all unmatched domains.
Waiting for verification…
Challenge failed for domain server.domain.gr
http-01 challenge for server.domain.gr
Cleaning up challenges
Some challenges have failed.
IMPORTANT NOTES:

DNS-based validation failed :
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator manual, Installer None
Obtaining a new certificate
Performing the following challenges:
dns-01 challenge for server.domain.gr
Running manual-auth-hook command: /etc/webmin/webmin/letsencrypt-dns.pl
Waiting for verification…
Challenge failed for domain server.domain.gr
dns-01 challenge for server.domain.gr
Cleaning up challenges
Running manual-cleanup-hook command: /etc/webmin/webmin/letsencrypt-cleanup.pl
Some challenges have failed.
IMPORTANT NOTES:

  • The following errors were reported by the server:

    Domain: server.domain.gr
    Type: unauthorized
    Detail: No TXT record found at _acme-challenge.server.domain.gr

    To fix these errors, please make sure that your domain name was
    entered correctly and the DNS A/AAAA record(s) for that domain
    contain(s) the right IP address.