Trying to sign in with Google in Firebase and getting an error

Question

I am simply trying to use sign in with Google in Firebase.

Error: "Unhandled Exception: PlatformException(sign_in_failed, com.google.android.gms.common.api.ApiException: 10: , null, null)"

I have it enabled and my SHA1 is added in the settings. I have all the required dependencies and applies as well as the .json file that is needed.

Here is my main.dart

import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  FirebaseAuth _auth = FirebaseAuth.instance;
  User _user;

  GoogleSignIn _googleSignIn = new GoogleSignIn();
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
          appBar: AppBar(
            title: Text("google Authentication"),
          ),
          body: isSignIn
              ? Center(
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      CircleAvatar(
                        backgroundImage: NetworkImage(_user.photoURL),
                      ),
                      Text(_user.displayName),
                      OutlineButton(
                        onPressed: () {
                          gooleSignout();
                        },
                        child: Text("Logout"),
                      )
                    ],
                  ),
                )
              : Center(
                  child: OutlineButton(
                    onPressed: () {
                      handleSignIn();
                    },
                    child: Text("Sign in with Google"),
                  ),
                )),
    );
  }

  bool isSignIn = false;

  Future<void> handleSignIn() async {
    GoogleSignInAccount googleSignInAccount = await _googleSignIn.signIn();
    GoogleSignInAuthentication googleSignInAuthentication =
        await googleSignInAccount.authentication;

    AuthCredential credential = GoogleAuthProvider.credential(
        idToken: googleSignInAuthentication.idToken,
        accessToken: googleSignInAuthentication.accessToken);

    var result = (await _auth.signInWithCredential(credential));

    _user = result.user;

    setState(() {
      isSignIn = true;
    });
  }

  Future<void> gooleSignout() async {
    await _auth.signOut().then((onValue) {
      _googleSignIn.signOut();
      setState(() {
        isSignIn = true;
      });
    });
  }
}

I am not sure why it is behaving like this and giving me an error.

Not sure why I have to add more text to compensate for the amount of code. Pretty much explained everything.