Implements Amplitude with flutter_segment package

We are trying to implement this package for segment and amplitude integration all at the flutter level.
https://pub.dev/packages/flutter_segment
https://pub.dev/packages/flutter_segment#setting-the-options-globally

The flutter_segment package to identify the user asks me for a session_id but when trying to get this session_id with the amplitude package it always returns -1.

My question is, what would be the best practice to integrate these two packages, maybe there is any suggestion?

As far as I understand I need to identify the user to get a session Id, maybe it works in a similar way with the anonimus id that segment provides?