I am following the tutorial given in the link https://www.digitalocean.com/community/tutorials/how-to-enable-digitalocean-private-networking-on-existing-droplets#ubuntu-1604 to set up private IP in the existing droplet.I added this

auto eth1
iface eth1 inet static
address DropletPrivateIP/16auto eth1
iface eth1 inet static
address DropletPrivateIP/16

I substituted the 'DropletPrivateIP' with my Pirvate IP and ran the command

"sudo systemctl restart networking"

Now I get the message

"Job for networking.service failed because the control process exited with error code. See "systemctl status networking.service" and "journalctl -xe" for details."

sadly the tutorial doe not say anything as what to do if we get any error message so here I want to ask what to do?

I ran the command "systemctl status networking.service" and I get:

● networking.service - Raise network interfaces
Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled
Drop-In: /run/systemd/generator/networking.service.d
└─50-insserv.conf-$network.conf
Active: failed (Result: exit-code) since Sun 2018-06-03 10:40:48 UTC; 3min 57s ago
Docs: man:interfaces(5)
Process: 6245 ExecStop=/sbin/ifdown -a --read-environment --exclude=lo (code=exited, sta
Process: 6328 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=1/FAILURE)
Process: 6321 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifq
Main PID: 6328 (code=exited, status=1/FAILURE)

Jun 03 10:40:46 Starting Raise network interfaces...
Jun 03 10:40:48 Waiting for DAD... Done
Jun 03 10:40:48 Cannot find device "eth1"
Jun 03 10:40:48 Failed to bring up eth1.
Jun 03 10:40:48 networking.service: Main process exited, code=ex
Jun 03 10:40:48 Failed to start Raise network interfaces.
Jun 03 10:40:48 networking.service: Unit entered failed state.
Jun 03 10:40:48 networking.service: Failed with result 'exit-cod
lines 1-19/19 (END)

Any help?

Thank you!