Reposting with correct service file:
[Unit]
Description=duplicati back-up service
[Service]
Environment=INSTALLDIR=/usr/lib/duplicati
Environment=LD_LIBRARY_PATH="${INSTALLDIR}${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
Environment=MONO_PATH="${MONO_PATH}:${INSTALLDIR}"
ExecStartPre=/usr/bin/sqlite3 /root/.config/Duplicati/Duplicati-server.sqlite "update option set value='' where Name='server-ssl-certificate';"
ExecStart=/usr/bin/duplicati-server --webservice-port=8200 --webservice-interface=0.0.0.0 --webservice-sslcertificatefile=/opt/certs/archive.pfx --log-file=/var/log/duplicati.log
[Install]
WantedBy=multi-user.target