DS1812+ backup to DNS-320 via rsync

[jackpalmer09]

Hi,
I'm trying to backup my DS1812+ to my DNS-320.
In the DNS-320, when I activate network backup, it asked me to input password only (no username).
However, when I setup on DS1812+, it asked me both username and password.
I have tried 'admin' as username but it failed when I pressed 'Test connection'.
Could anyone please guide me how to make it work?
Thanks.