Security.Authentication.AuthenticationException: The remote certificate is invalid according to the client validation

my code snippet attached here. i am not able to access i.e http client authentication getting failed can anyone suggest me on this. below mentioned error System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.Socket.Receive() at System.Net.Sockets.NetworkStream.Read(entities) --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Read(entities) at System.Net.FixedSizeReader.ReadPacket(entiryt) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob() at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult) at System.Net.TlsStream.CallProcessAuthentication(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result) at System.Net.TlsStream.Write()

       HttpWebRequest Request = (HttpWebRequest)WebRequest.Create("URL");
        Request.Method = "POST";
        Request.KeepAlive = false;

        Request.ContentType = postDataContentType;
        Request.Headers.Add(string.Format("Authorization: key={0}", apiKey));
        Request.Headers.Add(string.Format("Sender: id={0}", SENDER_ID));
        Request.ContentLength = byteArray.Length;

        Stream dataStream = Request.GetRequestStream();
        dataStream.Write(byteArray, 0, byteArray.Length);
        dataStream.Close();