Certificate error when logging in with FileZilla

Hello, I’m trying to access an FTP space of one of my sites via FileZilla. As soon as I connect, however, I get an expired certificate error. SSL for the domain is active and in fact if I search for the site from the browser everything is ok. Which certificate do I need to renew to avoid this problem? I’m new to this world and I’m not sure what to do.
The encryption I use on filezilla is “Use explicit FTP over TLS if available”
Thank you very much

SYSTEM INFORMATION
OS type and version Debian Linux 9
Webmin version 1.955
Usermin version 1.803
FileZilla version 3.59.0