Definitely, they all have their own nuances. 
systemctl enable duplicati works my friend, the issue is with the following file:
/usr/lib/systemd/system/duplicati.service
Using your text editor, nano, etc… modify this entry to look exactly like the above:
[Unit]
Description=Duplicati Backup software
[Service]
ExecStart=/usr/bin/mono /usr/lib/duplicati/Duplicati.Server.exe
Restart=on-failure
RestartSec=30
user=duplicati
group=duplicati
[Install]
WantedBy=multi-user.target
You have to remove the two lines for user duplicati and group duplicati.. IF you do not, duplicati will never run as root and therefore be unable to backup your system. For example, duplicati is installed but does not have access to the /home/tech folder, tech being my user account. However, after removing those two lines of code that are there by default, and restarting the service su root systemctl start duplicati … THEN and ONLY then does duplicati run as root and therefore have access to the ENTIRE disk.