Elixir and Firestore integration - cannot retrieve the document ID from Firestore

I am writing an application in Elixir and I have chosen Firestore as the database instead of Ecto/Postgres. There are two collections, user and job. Job is where users upload their task. The upload works fine.
Processing the task by the user takes about a minute and is being done by the python backend, then the result is put into Firestore. In the meantime, I am using polling to see when the results become available and search every few seconds.

The problem I am having is that I cannot retrieve the document ID from Firestore to understand which job to query. I cannot retrieve the right ID.

My workaround is now to try to set the ID already myself during upload, but maybe someone has done something similar before with Firebase?