I have a chat app where I create new keys dynamically. Within each dynamic key, when a user sends a message, I create an object inside that key with its own dynamic key.

The structure is as follows:

https://xxxxx-default-rtdb.europe-west1.firebasedatabase.app/
├── chrome%3A%2F%2Fextensions%2F -> dynamically created
    ├── -O-VkRKionPx9eGQs9fs -> dynamically created
        ├── createdAt: 1718536488277
        ├── name: "uur37484225"
        ├── text: "dsd"
        ├── uid: "itZx6OYhT9QqZHkGiZ29cvUEard2"

The following rules configuration doesn’t seem to be working:

{
  "rules": {
    ".read": "auth != null",
    ".write": "auth != null",
    "$url": {
      "$id": {
        ".indexOn": ["createdAt"]
      }
    }
  }
}

This is how I call the data:

const dbRef = ref(db, encodeFirebaseKey(currentUrl))
let queryRef

if (lastCreatedAt) {
  queryRef = query(dbRef, orderByChild("createdAt"), limitToLast(20))
} else {
  queryRef = query(dbRef, orderByChild("createdAt"), limitToLast(20))
}

get(queryRef)
  .then((snapshot) => {
    // Handle the snapshot
  })
  .catch((error) => {
    console.error("Error fetching messages:", error)
  })

The error I’m getting is:

Error: Index not defined, add ".indexOn": "createdAt", for path "/chrome%3A%2F%2Fextensions%2F", to the rules

What seems to be problem? I couldn’t really find any documentation about this issue