SSL certificate hostname does not match, but online validation says all is OK

Question

I secured our server with Let's Enccrypt SSL certificate, which I installed with Certbot on Apache. It works great - I validated it with online SSL checkers.

However, Filezilla FTP client always shows a message:

Uknown certificate | my.domain.com:21 - Hostname does not match certificate

If I accept it and ignore the warning, it still works, but I don't think it's a good security practice.

I ran hostname on Linux server and it's set correctly to "my.domain.com". I've also ran sudo certbot certificates to see Certbot certificates and it looks OK:

john123@my:~$ sudo certbot certificates
[sudo] password for john123:
Saving debug log to /var/log/letsencrypt/letsencrypt.log

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Found the following certs:
  Certificate Name: my.domain.com
    Domains: my.domain.com
    Expiry Date: 2021-07-12 01:43:40+00:00 (VALID: 48 days)
    Certificate Path: /etc/letsencrypt/live/my.domain.com/fullchain.pem
    Private Key Path: /etc/letsencrypt/live/my.domain.com/privkey.pem
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What could be the problem? See this screenshot for more details if needed:

Answer 1

FTP is a seperate service to https, normally handled with different software.

You likely need to update the certificate settings for the FTP server and restart it.