public void ListenToDocument(string collectionName, string documentId)
    {
        DocumentReference docRef = db.Collection(collectionName).Document(documentId);
        FirestoreChangeListener listener = docRef.Listen(snapshot =>
        {
            Console.WriteLine("Callback received document snapshot.");
            Console.WriteLine("Document exists? {0}", snapshot.Exists);
            if (snapshot.Exists)
            {
                Console.WriteLine("Document data for {0} document:", snapshot.Id);
                Dictionary<string, object> documentData = snapshot.ToDictionary();
                foreach (KeyValuePair<string, object> pair in documentData)
                {
                    Console.WriteLine("{0}: {1}", pair.Key, pair.Value);
                }
            }
        });
        listener.ListenerTask.Wait(); // Block until the listener is done

     public void ListenToDocument(string collectionName, string documentId)
    {
        DocumentReference docRef = db.Collection(collectionName).Document(documentId);
        FirestoreChangeListener listener = docRef.Listen(snapshot =>
        {
            Console.WriteLine("Callback received document snapshot.");
            Console.WriteLine("Document exists? {0}", snapshot.Exists);
            if (snapshot.Exists)
            {
                Console.WriteLine("Document data for {0} document:", snapshot.Id);
                Dictionary<string, object> documentData = snapshot.ToDictionary();
                foreach (KeyValuePair<string, object> pair in documentData)
                {
                    Console.WriteLine("{0}: {1}", pair.Key, pair.Value);
                }
            }
        });
        listener.ListenerTask.Wait(); // Block until the listener is done