Unable to retrieve Firebase Realtime Database entries

Currently, my data is stored in such structure:

Firebase Database 
|__Posts
    |__3Csdsadq931j(Post hash)
      |__1
        |__created: 1623414664 (timestamp)
           message: "Hello"
           msgID: 1
      |__2
        |__created: 1623414667 (timestamp)
           message: "Bye"
           msgID: 2

Currently, I have the posted hash of the chatroom. I would like to retrieve the posts by the most recent post, so from msgID 2 to 1.

However, I keep getting this failure message. "FIREBASE QUERY ERROR: Unable to get latest value for query FQuerySpec"

Here is my query:

// For this example: let postRoomID = "3Csdsadq931j"
let postReference: DatabaseReference = Database.database().reference().child("Posts").child(postRoomID)

postReference.queryOrdered(byChild: "created").queryLimited(toLast: 30).getData {error , snapshot in ...}

What am I doing wrong?