firebase didnt add data using flutter app

the url showing error giving me cast error. i am using realtime database and i also use

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

  }
}

when i add data the data is being saved in the app but post request didn't save it in the firebase
i creating this app form acedemine course.
The URL is correct .The URL is accessible from your my location or network.The server is running or maintenance. i want to resolve this issue,

  import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

import './product.dart';

class Products with ChangeNotifier {
  List<Product> _items = [
    Product(
      id: 'p1',
      title: 'Red Shirt',
      description: 'A red shirt - it is pretty red!',
      price: 29.99,
      imageUrl:
          'https://cdn.pixabay.com/photo/2016/10/02/22/17/red-t-shirt-1710578_1280.jpg',
    ),
    Product(
      id: 'p2',
      title: 'Trousers',
      description: 'A nice pair of trousers.',
      price: 59.99,
      imageUrl:
          'https://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Trousers%2C_dress_%28AM_1960.022-8%29.jpg/512px-Trousers%2C_dress_%28AM_1960.022-8%29.jpg',
    ),
    Product(
      id: 'p3',
      title: 'Yellow Scarf',
      description: 'Warm and cozy - exactly what you need for the winter.',
      price: 19.99,
      imageUrl:
          'https://live.staticflickr.com/4043/4438260868_cc79b3369d_z.jpg',
    ),
    Product(
      id: 'p4',
      title: 'A Pan',
      description: 'Prepare any meal you want.',
      price: 49.99,
      imageUrl:
          'https://upload.wikimedia.org/wikipedia/commons/thumb/1/14/Cast-Iron-Pan.jpg/1024px-Cast-Iron-Pan.jpg',
    ),
  ];
 

  List<Product> get items {
 
    return [..._items];
  }

  List<Product> get favoriteItems {
    return _items.where((prodItem) => prodItem.isFavorite).toList();
  }

  get id => null;

  Product findById(String id) {
    return _items.firstWhere((prod) => prod.id == id);
  }



  void addProduct(Product product) {
    const url =
        "https://flutter-update-'this place is hide by me'firebasedatabase.app/Products.json";
    http.post(
      url ,
      body: json.encode({
        'title ': product.title,
        'description': product.description,
        'imageUrl': product.imageUrl,
        'price': product.price,
        'isFavorite': product.isFavorite
      }),
    );

    final newProduct = Product(
      title: product.title,
      description: product.description,
      price: product.price,
      imageUrl: product.imageUrl,
      id: DateTime.now().toString(),
    );
    _items.add(newProduct);

    notifyListeners();
  }

  void updateProduct(String id, Product newProduct) {
    final prodIndex = _items.indexWhere((prod) => prod.id == id);
    if (prodIndex >= 0) {
      _items[prodIndex] = newProduct;
      notifyListeners();
    } else {
      print('...');
    }
  }

  void deleteProduct(String id) {
    _items.removeWhere((prod) => prod.id == id);
    notifyListeners();
  }
}

Your database security rules require that there is an authenticated user ("auth != null") in order to access the data.

But in your http.post call you don't specify any authentication credentials, which means that it is an anonymous user. So the security rules correctly reject that request.

To make http.post call come from an authenticated user, you'll need to pass a token as shown in the documentation on authenticating REST requests.

Firebase is not allowing post requests using external packages such as http. You should instead use the firebase_database api. Link for the documentation here: https://firebase.flutter.dev/docs/database/start