I have followed all the steps from here, I also added the SHA1 key in firebase console.

This is my code

void handleGoogleSignIn() async {
   String errorMessage = "success";

   GoogleSignInAccount _googleSignInAccount = await _googleSignIn.signIn();
   GoogleSignInAuthentication googleSignInAuthentication =
   await _googleSignInAccount.authentication;
   AuthCredential _credential = GoogleAuthProvider.getCredential(
       idToken: googleSignInAuthentication.idToken,
       accessToken: googleSignInAuthentication.accessToken);
   try {
     AuthResult _authResult = await _auth.signInWithCredential(_credential);
   } catch (error) {
     switch (error.code) {
       case "ERROR_INVALID_CREDENTIAL":
         errorMessage = "Invalid credentials";
         break;
       case "ERROR_ACCOUNT_EXISTS_WITH_DIFFERENT_CREDENTIAL":
         errorMessage = "This accouont exists withother credentials";
         break;
       case "ERROR_OPERATION_NOT_ALLOWED":
         errorMessage = "Signing in with Email and Password is not enabled.";
         break;
       default:
         errorMessage = "An undefined Error happened.";
     }
   }
   showErrorOrNavigate(errorMessage);
 }

I created a debug. keystore by following these steps

Exception: PlatformException(sign_in_failed, com.google.android.gms.common.api.ApiException: 10: , null) E/flutter (30467): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7) E/flutter (30467): #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:321:33) E/flutter (30467): E/flutter (30467): #2 MethodChannel.invokeMapMethod (package:flutter/src/services/platform_channel.dart:349:48) E/flutter (30467): #3 MethodChannelGoogleSignIn.signIn (package:google_sign_in_platform_interface/src/method_channel_google_sign_in.dart:45:10)`

Proof of SHA1 key added in firebase console:

I am not able to find my mistake.