What does ConnectionProviderError means in Amplify AppSync in Flutter SDK

Question

We are using Flutter SDK for Amplify AppSync for using Real Time Subscription.

https://pub.dev/packages/amplify_api

Sometime we receive error on AppSync subscription. As mentioned below

Error thrown ApiException(message: Subscription item event failed with error: Unauthorized, recoverySuggestion: , underlyingException: The operation couldn’t be completed. (AppSyncRealTimeClient.ConnectionProviderError error 5.)).

Error thrown ApiException(message: Subscription item event failed with error, recoverySuggestion: , underlyingException: The operation couldn’t be completed. (AppSyncRealTimeClient.ConnectionProviderError error 4.)).

I tried to figure out what does the error 4 and error 5 means, but was unable to do so.

I checked their swift SDK for ConnectionProvider

https://github.com/aws-amplify/aws-appsync-realtime-client-ios/tree/main/AppSyncRealTimeClient/ConnectionProvider

https://github.com/aws-amplify/aws-appsync-realtime-client-ios/blob/main/AppSyncRealTimeClient/ConnectionProvider/ConnectionProviderError.swift

But I could not figure out the cause for error. Can someone please help to identify when those error will be thrown. Thanks