How to fix Firebase Database connection was forcefully killed by the server error?

Question

firebase

I'm trying to make chat on flutter + firebase. Never worked with firebase. I created a project and databases through the Google console, configured everything according to the instructions from there. Chat on flutter did according to this guide. An error appears on startup:

W/PersistentConnection(11067): pc_0 - Firebase Database connection was forcefully killed by the server. Will not attempt reconnect. Reason: Database lives in a different region. Please change your database URL to https://my-testing-project-1020a-default-rtdb.europe-west1.firebasedatabase.app

Here is the complete code:

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/material.dart';
import 'package:intl/intl.dart' show DateFormat;

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  try {
    await Firebase.initializeApp();    
    runApp(MyApp());
  } catch (e) {
    print(e);
  }
}

class MyApp extends StatelessWidget {
  final _firebaseRef = FirebaseDatabase().reference().child('сhats');
  final _txtCtrl = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('My chat')),
        body: Container(
          child: Center(
            child: Column(
              children: [
                Directionality(
                  textDirection: TextDirection.ltr,
                  child: StreamBuilder(
                    stream: _firebaseRef.onValue,
                    builder: (context, snap) {
                      print(snap);

                      if (snap.hasData && !snap.hasError) {
                        final event = snap.data as Event;
                        Map data = event.snapshot.value;

                        List item = [];

                        data.forEach((index, data) => item.add({"key": index, ...data}));

                        return ListView.builder(
                          scrollDirection: Axis.vertical,
                          shrinkWrap: true,
                          itemCount: item.length,
                          itemBuilder: (context, index) {
                            return ListTile(
                              title: Text(item[index]['message']),
                              trailing: Text(DateFormat("hh:mm:ss")
                                  .format(DateTime.fromMicrosecondsSinceEpoch(item[index]['timestamp'] * 1000))
                                  .toString()),
                              onTap: () => updateTimeStamp(item[index]['key']),
                              onLongPress: () => deleteMessage(item[index]['key']),
                            );
                          },
                        );
                      } else {
                        return Text('No data');
                      }
                    }
                  ),
                ),
                Container(child: Row(children: <Widget>[
                  Expanded(child: TextField(controller: _txtCtrl)),
                  SizedBox(
                    width: 80,
                    child: OutlinedButton(
                      child: Text("Add", textDirection: TextDirection.ltr),
                      onPressed: () => sendMessage()
                    ),
                  )
                ]))
              ],
            ),
          ),
        ),
      ),
    );
  }

  sendMessage() {
    _firebaseRef.push().set({
      "message": _txtCtrl.text,
      "timestamp": DateTime.now().millisecondsSinceEpoch
    });
  }

  updateTimeStamp(key) {
    _firebaseRef.child(key).update({"timestamp": DateTime.now().millisecondsSinceEpoch});
  }

  deleteMessage(key) {
    _firebaseRef.child(key).remove();
  }
}