C# How to Access Asp.net Label value from array type Webmethode?

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I want to call array type methode from jquery so below code is working fine.

<script type="text/javascript">
        $(document).ready(function () {
            $("#tblCustomers tbody tr").remove();
            $.ajax({
                type: "POST",
                url: "GetDataByJquery.aspx/GetMessages",
                data: '{roomId: "' + $("#lblRoomId").val() + '" }',
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (data) {
                    response($.map(data.d, function (item) {
                        var rows = "<tr>"
                    + "<td class='customertd'>" + item.Username + "</td>"
                    + "<td class='customertd'>" + item.Sex + "</td>"
                    + "<td class='customertd'>" + item.Text + "</td>"
                    + "<td class='customertd'>" + item.TimeStamp + "</td>"
                    + "<td class='customertd'>" + item.UserID + "</td>"
                    + "</tr>";
                        $('#tblCustomers tbody').append(rows);
                    }))
                },
                failure: function (response) {
                    alert(response.d);
                }
            });
        });
    </script>

so in this I cant get label control value to pass below webmthode.

[WebMethod]
        public static Messages[] GetMessages(string roomId)
        {
            List<Messages> messages = new List<Messages>();           
            string strConnString = ConfigurationManager.ConnectionStrings["LinqChatConnectionString"].ConnectionString;

            using (SqlConnection con = new SqlConnection(strConnString))
            {
                using (SqlDataAdapter sda = new SqlDataAdapter())
                {
                    string query = "[Get_Messages]";
                    SqlCommand cmd = new SqlCommand(query);
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.AddWithValue("@roomId", roomId);
                    cmd.Connection = con;
                    sda.SelectCommand = cmd;
                    con.Open();
                    SqlDataReader reader = cmd.ExecuteReader();

                    while (reader.Read())
                    {
                        Messages message = new Messages();
                        message.Username = reader.GetString(0);
                        message.Sex = reader.GetString(1);
                        message.Text = reader.GetString(2);
                        message.TimeStamp = reader.GetString(3);
                        message.UserID = reader.GetString(4);
                        messages.Add(message);
                    }
                }
            }
            return messages.ToArray();
        }

So how to pass asp.net label control value to 'GetMessages' methode's parameter?