Certbot certificate renewal error

Hello forum!
I have an issue with my ncp: obviously there’s something wrong with my certificates. Thunderbird and Firefox say that the certificate has expired. I thought I’ve configured it to renew automatically an so says the NCP panel (Your certificate will be automatically renewed every month). And:

    [ letsencrypt ]
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Cert not yet due for renewal
Keeping the existing certificate

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Certificate not yet due for renewal; no action taken.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
System config value trusted_domains => 4 set to string nc.net
System config value overwrite.cli.url set to string https://nc.net/

I have an NC-Message that says that the SSL certificate renewal failed. See /var/log/letsencrypt/letsencrypt.log. In the log I’ve found that there’s an issue with the /etc/letsencrypt/renewal/nc.net.conf file. I’ve had a look at it and it is empty. There’s a file /etc/letsencrypt/renewal/nc.net-0001.conf with a few lines in it. I don’t know what this file really should look like to work proper.

Where can I start searching for a solution?

Yours

SMichel