Command line for Dropbox connection in Duplicati backup

See more:

backup

command-line

DropBox

I m trying to backup Folders from local drive to Dropbox using Duplicati command in Command prompt. (Backup should be Incremental)

C:\Users\Desktop\Office_Works\Duplicati\Duplicati 1.3.4\Duplicati>Duplicati.CommandLine.exe backup a https://www.dropbox.com/

Enter passphrase: **
Confirm passphrase: **
**Unable to find backend for: https://www.dropbox.com/**

"a" is my folder in local drive. Now I want to know how to make a connection with Dropbox using command lines. Is any particular way to connect Dropbox using duplicati commands?

Thanks in Advance!