What you showed above is rsync utilizing SSH using password authentication. If you want this to work in an automated fashion you need to enable 'public key authentication'. Simply follow the link again and see @subzero79's explanation.
Looks like you’re pushing against another rsync server, with modules defined. The user/password is the one defined in modules not Pam or Linux user account (at least from the point of view is Omv was the rsyncd server). I am guessing some is misconfigred at Synology.
Strange that is failing, sure the password is correct ?