Getting a certificate error or warning when connecting via FTP using TLS?

This error usually occurs when an FTP client (like Filezilla) is using using a secure connection to the ftp server under a custom hostname.

It’s nothing to worry about, the certificate for ‘ftp.stackcp.com’ is expected so you can trust the certificate with the knowledge that the connection will remain encrypted. Once the ceritifcate is trusted you should not receive any further warnings, unless the certificate changes.

To avoid the warning altogether, you could change the FTP hostname to use the ftp.stackcp.com hostname.