Ajaxtoolkit - Autocomplete dont do anything when i click - asp.net

Question

I have tried everything and nothing works, i have no clue now. I used an example, that used to work ones but dont anymore. I used this example
https://www.aspsnippets.com/Articles/AJAX-AutoCompleteExtender-Example-in-ASPNet.aspx
And download the ajaxtoolkit from here
https://www.devexpress.com/products/ajax-control-toolkit/
I have scriptmanager in the top of the page and it looks like this.
This is my code
Masterpage.master
<asp:TextBox ID="txtContactsSearch" aria-describedby="basic-addon2" class="form-control-header" placeholder="Søg her ..." runat="server"></asp:TextBox> <cc1:AutoCompleteExtender ServiceMethod="SearchCustomers" MinimumPrefixLength="2" ServicePath="MasterPage.master" CompletionInterval="100" EnableCaching="false" CompletionSetCount="10" TargetControlID="txtContactsSearch" ID="AutoCompleteExtender1" runat="server" FirstRowSelected = "false"></cc1:AutoCompleteExtender>
My codebehind
[System.Web.Script.Services.ScriptMethod()]
[System.Web.Services.WebMethod]
public static List<string> SearchCustomers(string prefixText, int count)
{
using (MySqlConnection conn = new MySqlConnection())
{
conn.ConnectionString = ConfigurationManager.ConnectionStrings["Connectionstring"].ConnectionString;
using (MySqlCommand cmd = new MySqlCommand())
{
cmd.CommandText = "select Produktnavn from Produkter where " +
"Produktnavn like #SearchText + '%'";
cmd.Parameters.AddWithValue("#SearchText", prefixText);
cmd.Connection = conn;
conn.Open();
List<string> customers = new List<string>();
using (MySqlDataReader sdr = cmd.ExecuteReader())
{
while (sdr.Read())
{
customers.Add(sdr["Produktnavn"].ToString());
}
}
conn.Close();
return customers;
}
}
}