When using TLS you need to verify the certificate of the server. That is what the error is saying, could not verify the certificate. You need to edit the /etc/lftp.conf file and add this line:

set ssl:ca-file "/etc/ssl/certs/ca-certificates.crt"

You must then also copy the ca of the server to your router as /etc/ssl/certs/ca-certificates.crt

Should work after that :slight_smile: