Firebase Database query

This is my Flutter Firebase database structure.

final notesReference = FirebaseDatabase.instance.reference();
await notesReference.child("data").orderByChild("displayDescription").equalTo('23').once().then(

Result is nothing, list is empty. Why?

Without equalTo('23') it works fine. I also try to change my Firebase rules

{
"rules": {
     ".read": true,
     ".write": true,    
     "data" : {
         ".indexOn": ["displayDescription"]
     }

    }
}

I just want where displayDescription = "23"

I think child of 'displayDescription' is not a string. But, you are querying a string '23'. Try parse string or remove '' sign