Open up the url https://<IPAdress>:9443/ssg/backup in your browser, it will list all the nodes in the cluster. Select the click on the node name to download the backup. Or else use the same node name from a script or command line utility. Usually the node names are not same as the I.P. Address, by default they will be Gateway1, Gateway2 etc, and in some cases they are renamed by administrators. From my experience the easiest way to find out is to open the backup url on a browser. From your attachment it looks like you are using Gateway1 as node name.
Regards,
Anand