im doing an C# app with .NET Windows Forms Framework and i have a permission dennied error when i try to send information to realtime db, but im have logged in in the app. The security of my Firebase Realtime DB is the following:

{
  "rules":{
    ".read": "auth.uid != null",
    ".write": "auth.uid != null"
  }
}

im using FirebaseAuthentication.net (v3.7.1) and FirebaseDatabase.net (v4.2.0) from Step Up Labs

using Firebase.Database;
using Firebase.Database.Query;
using Firebase.Auth;

the code where the Permission Dennied Errors ocurred is the following

private async void button_reg_Click(object sender, EventArgs e)
{
    authProvider = new FirebaseAuthProvider(new FirebaseConfig("my_api_key"));


    var authResult = await authProvider.SignInWithEmailAndPasswordAsync("a mail that exists on firebase auth", "the correct password");


    if (authResult != null)
    {
        var user = new Users()
        {
            Address = "Country",
            LastName = "Doe",
            Name = "John"
        };

        var client = getFirebaseClient();

        await client.Child(nameof(Users))
            .PostAsync(user);
    }    
}

private FirebaseClient getFirebaseClient()
{
    return new FirebaseClient("my_database_url");
}

class users is

 public class Users
 {
     public string Name { get; set; }
     public string LastName { get; set; }
     public string Key { get; set; }
     public string Address { get; set; }
 }

the code passes authResult!=null but then in this line “await client.Child(nameof(Users))
.PostAsync(user);” the following error ocurres

Firebase.Database.FirebaseException: 'Exception occured while processing the request.
Url: https://project-projectNumber-default-rtdb.firebaseio.com/Users/-NwVBBRKfhiWk5R1ISC5/.json?print=silent
Request Data: {"Name":"John","LastName":"Doe","Key":null,"Address":"Country"}
Response: {
  "error" : "Permission denied"
}
'

i dont understand where the problem is, i hope someone have the answer