How to add Document to a SubCollection

Hi,

I am starting to use the Firebase collection and subcollection integrations in Flutterflow.

I just created a collection and subcollection schemas following the official doc
https://docs.flutterflow.io/data-and-backend/firebase/firestore-database-cloud-firestore/creating-subcollections

everything goes smoothly until I want to add documents. I clicked on Manage Content, but I only can add content to the collections, the subcollection just doesn't appear on the list tree on the left.

Could you please tell me how to do this?

Thanks a lot