I run a few FTP servers that use Pure-FTPD with TLS on it for extra security, and on the ones that don’t have a “real” SSL cert, you will see the following when using LFTP and trying a “ls”:
ls: Fatal error: Certificate verification: Not trusted
The way to work around that is to add the following to your “.lftp/rc” file:
set ssl:verify-certificate no
And you are good to go!