Flutter Firebase Auth: A network error (such as timeout, interrupted connection or unreachable host) has occurred

In my case I solved allowing Outgoing Connections on the Xcode's Runner.xcworkspace

In my case, my VPN was causing the problem. Disabling the VPN and testing it again solved the error. I hope it helps.

if you are trying this out in a simulator, then this error may pop up as the internet of your simulator is not connected. To solve this you can run your app on a physical device and it will work!

Normally when the emulator is doing a lot of work on the thread, it tends to misbehave, such a losing internet connectivity even if your PC is well connected. My suggestion(Which worked for me) is you kill the emulator, and go to Android Studio AVD Manager and Wipe Data for that Emulator, then restart the Emulator, it worked for me. Kindly find below the image screenshot

Open Terminal in the project folder, run the following two commands:

adb kill-server
    
adb start-server

If adb is not recognized, add C:\Users\USERNAME\AppData\Local\Android\Sdk\platform-tools to environement variables.

I am late to the party but I found another solution.

If using an android emulator, disabling the Android Studio HTTP proxy settings can restore the network connection.

import 'package:badam/varify.dart';
import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'dart:async';

import 'HomePage.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'FireBase Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new LoginPage(),
      routes: <String, WidgetBuilder>{
        '/loginpage' : (BuildContext context) => Dash(),
        '/landpage' : (BuildContext context) => LoginPage(),
    }
    );
  }
}
class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  String phoneNo, smsId, verificationId;

  Future<void> verifyPhone() async{
    final PhoneCodeAutoRetrievalTimeout autoRetrieve = (String verId){
      this.verificationId = verId;
    };
    final PhoneCodeSent smsCodeSent = (String verId, [int forceCodeResend]){
      this.verificationId = verId;
      smsCodeDialoge(context).then((value){
        print('Signed In');
      });
    };
    final PhoneVerificationCompleted verifiedSuccess = (AuthCredential auth){
      print('verified');
    };
    final PhoneVerificationFailed verifyFailed = (AuthException e) {
      print('${e.message}');
    };
    await FirebaseAuth.instance.verifyPhoneNumber(
      phoneNumber: phoneNo,
      timeout: const Duration(seconds: 5),
      verificationCompleted: verifiedSuccess,
      verificationFailed: verifyFailed,
      codeSent: smsCodeSent,
      codeAutoRetrievalTimeout: autoRetrieve,
    );
  }
  Future<bool> smsCodeDialoge(BuildContext context){
    return showDialog(context: context,
      barrierDismissible: false,
      builder: (BuildContext context) {
        return new AlertDialog(
          title: Text('Enter OTP'),
          content: TextField(
            onChanged: (value)  {
              this.smsId  = value;
            },
          ),
          contentPadding: EdgeInsets.all(10.0),
          actions: <Widget>[
            new FlatButton(
                onPressed: (){
                  FirebaseAuth.instance.currentUser().then((user){
                    if(user != null){
                      Navigator.of(context).pop();
                      Navigator.push(
                        context,
                        MaterialPageRoute(builder: (context) => Dash()),
                      );

                    }
                    else{
                      Navigator.of(context).pop();
                      signIn(smsId);
                    }

                  }
                  );
                },
                child: Text('Done', style: TextStyle( color: Colors.blue),))
          ],
        );
      },
    );
  }

  Future<void> signIn(String smsCode) async {
    final AuthCredential credential = PhoneAuthProvider.getCredential(
      verificationId: verificationId,
      smsCode: smsCode,
    );
     await FirebaseAuth.instance.signInWithCredential(credential)
        .then((user){
      Navigator.of(context).pushReplacementNamed('/loginpage');
    }).catchError((e){
      print(e);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: Text('Sign In')
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,

        children: <Widget>[
          Text('Phone Auth',style: TextStyle(fontSize: 20,color: Colors.blue),),
          Padding(
            padding: const EdgeInsets.all(16.0),
            child: TextField(
              decoration: InputDecoration(
                hintText: 'Enter your phone number',
              ),
              onChanged: (value){
                this.phoneNo = value;
              },
            ),
          ),
          SizedBox(height: 10.0),
          RaisedButton(
            onPressed: verifyPhone,
            child: Text('Verify', style: TextStyle(color: Colors.white),),
            elevation: 7.0,
            color: Colors.blue,

          )
        ],
      ),
    );
  }
}

It worked for me, hope this helps you!