lftp Fatal error: Certificate verification: Not trusted

When I use lftp to transfer file between my Linux machine and my hosting server, I type the command in my Linux shell:

# lftp -u myuser,mypassword example.com
lftp myuser@example.com:~>ls
cd: Fatal error: Certificate verification: Not trusted

The problem is the server certificate it not valid on the server. To override this error forever, I just created file in my home folder.

# vim .lftp/rc
set ssl:verify-certificate no

Then, I got next error from lftp console.

Access failed : 521 Data connection cannot be opened with this PROT setting.

In tne file “.lftp/rc” I added more lines with:

set ftp:ssl-force true
set ftp:ssl-protect-data true

The problem then gone, and I can transfer the data from and to server without problem.