Best in ringing your local 3CX support number
Hello @mic.max
Are you using your own or a 3CX provided FQDN? Is this a local or hosted installation?
Please make sure that you can resolve activation.3cx.com and letsencrypt.org correctly when you perform an nslookup. Also did you get a email showing that your certificate did not update correctly?
Please send me a personal message with your FQDN so i can further look into the issue.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.