If you are planning to add events from your backend application and if you want to associate that event with the Growlytics Session, this article will guide you on how you can achieve that.
The Session identifier is nothing but the device id of the customer that Growlytics maintains. You can use
Growlytics.getDeviceId() to read the device id.
let deviceId = Growlytics.getDeviceId();
You can pass the device id received to your backend server and use it while adding an event to Growlytics from your backend.