The only issue I had was turning off the verify certificate and setting that to no.

$ lftp -p 990 bigbeav@ftps.servnername.com
Password:
lftp bigbeav@ftps.servername.com:~> ls
ls: Fatal error: Certificate verification: Not trusted
lftp bigbeav@ftps.servername.com:~> set ssl:verify-certificate no
lftp bigbeav@ftps.servname.com:~> ls
drwxr-xr-x 2 ftp ftp 48 Jan 21 21:24 bin
lftp bigbeav@ftps.servername.com:/>