Check Username availability in Page Load and keyup based on TextBox value using AJAX PageMethods in ASP.Net

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE PROCEDURE dbo.CheckUsername
     @Email VARCHAR(255)
AS
BEGIN
      SET NOCOUNT ON;
      IF NOT EXISTS
            (SELECT * FROM T_Create_Profile
             WHERE Email = @Email
            )
            SELECT 'true'
      ELSE
            SELECT 'false'
END
GO


<System.Web.Services.WebMethod()> _
    Public Shared Function CheckUserName(ByVal userName As String) As String
        Dim returnValue As String = String.Empty
        Try
            Dim consString As String = ConfigurationManager.ConnectionStrings("ConString").ConnectionString
            Dim conn As New SqlConnection(consString)
            Dim cmd As New SqlCommand("CheckUsername", conn)
            cmd.CommandType = CommandType.StoredProcedure
            cmd.Parameters.AddWithValue("@Username", userName.Trim())
            conn.Open()
            returnValue = cmd.ExecuteScalar().ToString()
            conn.Close()
        Catch
            returnValue = "error"
        End Try
        Return returnValue
    End Function

<script type="text/javascript">
        function UsernameAvailability() {
            PageMethods.CheckUserName(document.getElementById("<%=txtUsername.ClientID%>").value, Username_OnSuccess);
        }
        function Username_OnSuccess(response) {
            var mesg = document.getElementById("Username_Check");
            
            switch (response) {
                case "true":
                    mesg.style.color = "";
                    mesg.innerHTML = "";
                    break;
                case "false":
                    mesg.style.color = "red";
                    mesg.innerHTML = "Username already taken.";
                    break;
            }
        }
        function Username_OnChange(txt) {
            document.getElementById("Username_Check").innerHTML = "";
        }
    </script>

                            
<span id="Username_Check"></span>

                            
<asp:TextBox ID="txtUsername" runat="server" onkeyup="Username_OnChange(this);UsernameAvailability();" ondrop="return false;" onpaste="return false;"></asp:TextBox>

I created a table called T_Create_Profile and in the table I added a column called Username. Then I added a data under Username called Will. Now After I run the program and typed “Will” into the textbox I was hoping to see the message saying “Username already taken” but I don’t see any message. Am I doing anything wrong?

By the way I tried to follow one of your tutorials titled “Check Username Availability in ASP.Net using AJAX PageMethods” but no luck. Please help.