GraphQL.Client Subscription Error from Xamarin

Hi everyone,
I have a proof of concept on AppSync/GraphQL.Client.
I am successfully querying and creating GraphQL mutations. However, I get an error when trying to subscribe.

**Error**:
`
Unable to connect to the remote server
`
**Stack Trace**:
```
at System.Net.WebSockets.WebSocketHandle.ParseAndValidateConnectResponseAsync (System.IO.Stream stream, System.Net.WebSockets.ClientWebSocketOptions options, System.String expectedSecWebSocketAccept, System.Threading.CancellationToken cancellationToken) [0x00100] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.Net.WebSockets.Client/src/System/Net/WebSockets/WebSocketHandle.Managed.cs:337
at System.Net.WebSockets.WebSocketHandle.ConnectAsyncCore (System.Uri uri, System.Threading.CancellationToken cancellationToken, System.Net.WebSockets.ClientWebSocketOptions options) [0x00383] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.Net.WebSockets.Client/src/System/Net/WebSockets/WebSocketHandle.Managed.cs:148
at System.Net.WebSockets.ClientWebSocket.ConnectAsyncCore (System.Uri uri, System.Threading.CancellationToken cancellationToken) [0x000d1] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.Net.WebSockets.Client/src/System/Net/WebSockets/ClientWebSocket.cs:157
at GraphQL.Client.Http.Websocket.GraphQLHttpWebSocket.ConnectAsync (System.Threading.CancellationToken token) [0x000ff] in <5343ffaac4864176b8f7c0b9cc6d172c>:0
```

I was [reading on AWS App Sync documentation](https://docs.aws.amazon.com/appsync/latest/devguide/real-time-websocket-client.html) that the web socket URL is different from the GraphQL Endpoint.

I am trying to follow the example from the [integration test](https://github.com/graphql-dotnet/graphql-client/blob/master/SubscriptionIntegrationTest.ConsoleClient/Program.cs)

**Code**

```
public static void CreateSubscription()
{
var subscriptions = new CompositeDisposable();

subscriptions.Add(Client.WebSocketReceiveErrors.Subscribe(e =>
{
if (e is WebSocketException we)
Console.WriteLine($"WebSocketException: {we.Message} (WebSocketError {we.WebSocketErrorCode}, ErrorCode {we.ErrorCode}, NativeErrorCode {we.NativeErrorCode}");
else
Console.WriteLine($"Exception in websocket receive stream: {e.ToString()}");
}));

subscriptions.Add(CreateSubscription("1"));

}

private static IDisposable CreateSubscription(string id)
{
var taskCreatedRequest = new GraphQLRequest
{
Query = @"
subscription {
onCreateTasksPocModel{
id
description
date
}
}",
Variables = new
{
id
}
};

IObservable> subscriptionStream
= Client.CreateSubscriptionStream(taskCreatedRequest);

var subscription = subscriptionStream.Subscribe(
response => {
Console.WriteLine($"new message from \"{response}\": {response}");
},
exception => {
Console.WriteLine($"message subscription stream failed: {exception}");
},
() =>
{
Console.WriteLine($"message subscription stream completed");
});
return subscription;
}

static GraphQLHttpClient CreateClient()
{
var graphQLOptions = new GraphQLHttpClientOptions()
{
EndPoint = new Uri(GraphQLConstants.GraphQLApiUrl), //https://
//AppSync real-time endpoint from the AWS AppSync GraphQL endpoint is different for websocket
//as per https://docs.aws.amazon.com/appsync/latest/devguide/real-time-websocket-client.html
WebSocketEndPoint = new Uri(GraphQLConstants.GraphQLSocketUrl),//wss://
HttpMessageHandler = new NativeMessageHandler(),
UseWebSocketForQueriesAndMutations =true
};

var client = new GraphQLHttpClient(graphQLOptions, new NewtonsoftJsonSerializer());
client.HttpClient.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue(new ProductHeaderValue(nameof(MobileGraphql))));
client.HttpClient.DefaultRequestHeaders.Add(GraphQLConstants.ApiKeyName, GraphQLConstants.ApiKeyValue);
client.HttpClient.DefaultRequestHeaders.Host = GraphQLConstants.GraphQLHost;
return client;
}
```

[View Full Source Code (Gist](https://gist.github.com/henry-delgado/0cfe837e935b51d77f919263e25fe1ae)

I have read similar issues such #333 but that has not helped and wonder if anyone could help me out.

Thanks