In Duplicati 1 I can do it via command line. I can a backup or a backup group. Have Duplicati 2 same command line parameters?
I’m assuming you mean starting a backup, from the command line, on your Duplicati server as if you had pressed “Run now” in the Web GUI.
There’s an issue on Github for command line control of the Duplicati server here: Integration between command line and web interface · Issue #2693 · duplicati/duplicati · GitHub
It more or less boils down to the command line and the server being incompatible in the sense that they do not communicate at all. It’s easier to implement a new command line client than it is to repurpose the existing command line (which serves other purposes).
I’ve made a proof of concept of how I think such a client could look. It’s by no means tested software but it can do what you’re requesting.