Flutter – "Firebase Messaging getToken() Error: Invalid fetch response, expected 'token' or 'Error' key" in ios app

I’m encountering an error when trying to get the token using Firebase Messaging in my Flutter iOS app. The error message is as follows:

FLTFirebaseMessaging: An error occurred while calling method Messaging#getToken, errorOrNil => {    NSLocalizedFailureReason = "Invalid fetch response, expected 'token' or 'Error' key";}

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: [firebase_messaging/unknown] An unknown error has occurred.
#0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:651:7)
#1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:334:18)
<asynchronous suspension>
#2      MethodChannel.invokeMapMethod (package:flutter/src/services/platform_channel.dart:534:43)
<asynchronous suspension>
#3      MethodChannelFirebaseMessaging.getToken (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:248:11)
<asynchronous suspension>
#4      FCMToken.getFcm (package:instahire/firebase/fcm_token.dart:5:21)
<asynchronous suspension>
#5      SplashController.getToken (package:instahire/controllers/splash_controller.dart:42:23)
<asynchronous suspension>

Till yesterday it was working fine suddenly this error occurred.
How to solve this?