using (SqlConnection con = new SqlConnection(connectionString))
            {
                con.Open();
                string bruker = Request.Cookies["Navn"].Value;
                string mobilnr = Request.Cookies["Mobilnr"].Value;

                string commandText = "SELECT Engangskode FROM Brukere WHERE Navn=@navn AND Mobilnr=@mobilnr";

                bool correctCode = false;

                try
                {
                    using (SqlCommand command = new SqlCommand(commandText, con))
                    {
                        command.Parameters.Add("@navn", SqlDbType.NVarChar, 20).Value = bruker;
                        command.Parameters.Add("@mobilnr", SqlDbType.NChar, 10).Value = mobilnr;
                        using (SqlDataReader reader = command.ExecuteReader())
                        {
                            while (reader.Read())
                            {
                                if (TextBox1.Text == reader[0].ToString())
                                {
                                    correctCode = true;
                                }
                            }
                        }

                        if (correctCode)
                        {
                            commandText = "UPDATE Brukere SET Engangskode=CAST(NULL AS NCHAR) WHERE Navn=@navn AND Mobilnr=@mobilnr";
                            command.ExecuteNonQuery();

                            Response.Redirect("Kvittering.aspx",  false);
                        }
                    }
                }
                catch (Exception error)
                {
                    Console.WriteLine(error.Message);
                    //håndtere andre errors
                }
            }