AppSync's WS connection closing at initialization

I'm trying to follow the example listed in [this](https://github.com/graphql-dotnet/graphql-client/issues/372#issuecomment-990590565) previously closed issue with my own AppSync setup. However, when the code hits the `.InitializeWebSocketConnection`, I get a relatively vague WebSocketException saying `The remote party closed the WebSocket connection without completing the close handshake`. Here is my current code

```
public class AppSyncHeader
{
[JsonPropertyName("host")]
public string Host { get; set; }

[JsonPropertyName("x-api-key")]
public string ApiKey { get; set; }

public string ToJson()
{
return JsonSerializer.Serialize(this);
}

public string ToBase64String()
{
return Convert.ToBase64String(Encoding.UTF8.GetBytes(ToJson()));
}
}

public class AuthorizedAppSyncHttpRequest : GraphQLHttpRequest
{
private readonly string _authorization;

public AuthorizedAppSyncHttpRequest(GraphQLRequest request, string authorization) : base(request) =>
_authorization = authorization;

public override HttpRequestMessage ToHttpRequestMessage(
GraphQLHttpClientOptions options,
IGraphQLJsonSerializer serializer
)
{
HttpRequestMessage result = base.ToHttpRequestMessage(options, serializer);
result.Headers.Add("X-Api-Key", _authorization);
return result;
}
}

public static async Task Main(string[] args)
{
var regularHost = "xxxxxx.appsync-api.us-east-1.amazonaws.com";
var wsHost = "xxxxxx.appsync-realtime-api.us-east-1.amazonaws.com";
var apiKey = "foobar";

var client = new GraphQLHttpClient(
$"https://{regularHost}/graphql",
new SystemTextJsonSerializer(
new JsonSerializerOptions() { PropertyNamingPolicy = JsonNamingPolicy.CamelCase }
)
);

var appSyncHeader = new AppSyncHeader { Host = regularHost, ApiKey = apiKey, };

string header = appSyncHeader.ToBase64String();

client.Options.WebSocketEndPoint = new Uri($"wss://{wsHost}/graphql?header={header}&payload=e30=");
client.Options.PreprocessRequest = (req, client) =>
{
GraphQLHttpRequest result = new AuthorizedAppSyncHttpRequest(req, apiKey)
{
["data"] = JsonSerializer.Serialize(req),
["extensions"] = new { authorization = appSyncHeader, }
};
return Task.FromResult(result);
};

await client.InitializeWebsocketConnection();
}
```

@rose-a would you happen to know? Perhaps there is something obvious that I am missing in the configuration or suggestion on how to debug the connection failure.