asp.net core send ping websocket closed

[SwaggerIgnore]
[Route("/ws")]
public async Task Open()
{
    if (HttpContext.WebSockets.IsWebSocketRequest)
    {
        using var webSocket = await HttpContext.WebSockets.AcceptWebSocketAsync();
        var buffer = new byte[1024 * 4];
        var receiveResult = await webSocket.ReceiveAsync(
        new ArraySegment<byte>(buffer), CancellationToken.None);

        if (receiveResult.Count == 0)
        {
            return;
        }

        var receivedMessage = Encoding.UTF8.GetString(buffer, 0, receiveResult.Count);

        char[] delimiters = new char[] { ' ', ',', '.' };
        string[] words = receivedMessage.Split(delimiters, StringSplitOptions.RemoveEmptyEntries);
        if(words.Length == 0)
        {
            Console.WriteLine($"{receivedMessage} | words 0");
            return;
        }
        Console.WriteLine($"{receivedMessage}");
        foreach (var item in words)
        {
            Debug.WriteLine(item);
        }

        string key = words[1];
        if (!GlobalCache._websocket.ContainsKey(key))
        {
            GlobalCache._websocket.Add(key, webSocket);
            Console.WriteLine($"{key} Websocket Add.");
        }

        await Echo(webSocket, key);
    }
    else
    {
        HttpContext.Response.StatusCode = StatusCodes.Status400BadRequest;
    }
}

private async Task Echo(WebSocket webSocket, string key)
{
    
    try
    {
        var buffer = new byte[1024 * 4];
        WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);

        while (!result.CloseStatus.HasValue)
        {
            await SendMessageAsync(webSocket, key, "ping");
            await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);
            result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
        }
        await webSocket.CloseOutputAsync(WebSocketCloseStatus.NormalClosure, "closing websocket", CancellationToken.None);
        //await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, "Error");
    }
    
}

private async Task SendMessageAsync(WebSocket webSocket, string key, string message)
{
    var messageBuffer = Encoding.UTF8.GetBytes(message);
    var segment = new ArraySegment<byte>(messageBuffer);

    await webSocket.SendAsync(segment, WebSocketMessageType.Text, true, CancellationToken.None);
}