I have an Flutter chat application.
The structure of FireStore is as below.
chats (collection) > roomId (random generated id, which is a document) > users (collection) > email (email of the user, which is a document) > messages (collection) > messageId (random generated id, which is a document) > the actual chat.

When I use the following code it works. This gives all the messages in a room by a particular user.

FirebaseFirestore.instance
        .collection('chats')
        .doc(roomId)
        .collection('users')
        .doc(user)
        .collection('messages')
        .orderBy('timestamp', descending: true)
        .snapshots(),

However, I need to get a list of all the users in a room. This is the code that I tried and is not getting any result, empty list.

QuerySnapshot<Map<String, dynamic>> userCollection = await FirebaseFirestore.instance
          .collection('chats')
          .doc(roomId)
          .collection('users')
          .get();

Here is the rule that is set on the store.

rules_version = '2';

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if true;
    }
  }
}

I need to get the list of all the users in the room.
Any help is appreciated.