Autocomplete jquery UI does not authenticate

Question

When i try to fire the autocomplete in my TextBox it return me this error:

localhost:44349 says:
{"Message":"
authentication failed","StackTrace":null,"ExceptionType":"System.InvalidOperationException"}

But my credentials are corrects, in fact i can connect directly using SSMS

I tried this:

These are the TextBox and his hidden field

<asp:TextBox runat="server" type="text" ID="searchInput" class="planningInput" placeholder="Cerca codice" />
<asp:HiddenField runat="server" ID="searchInputhf" />

This is my script:

 <script type="text/javascript">
     $(function () {
         $("[id$=searchInput]").autocomplete({
             source: function (request, response) {
                 $.ajax({
                     url: 'PlanningNAV.aspx/getAutocomplete',
                     data: "{ 'prefix': '" + request.term + "'}",
                     dataType: "json",
                     type: "POST",
                     contentType: "application/json; charset=utf-8",
                     success: function (data) {
                         response($.map(data.d, function (item) {
                             return {
                                 value: item.split(' |')[0]
                             }
                         }))
                     },
                     error: function (response) {
                         alert(response.responseText);
                     },
                     failure: function (response) {
                         alert(response.responseText);
                     }
                 });
             },
             select: function (e, i) {
                 $("[id$=searchInput]").val(i.item.val);
             },
             minLength: 3
         });
     });
 </script>

And in my code behind i got this:

 [WebMethod]
 [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
 public string[] getAutocomplete(string prefix)
 {
     List<string> codice = new List<string>();
     using (SqlConnection conn = new SqlConnection("Data Source = VMSRVDB01; Initial Catalog = ADIMPEX; Persist Security Info=True; User ID = user1; Password=User123; Integrated Security=True"))
     {
         
         using (SqlCommand cmd = new SqlCommand())
         {
             cmd.CommandText = "SELECT [Adimpex$Item].No_ FROM [Adimpex$Item] WHERE [Adimpex$Item].No_ LIKE ('%' + @SearchText + '%')";
             cmd.Parameters.AddWithValue("", prefix.ToUpper());
             cmd.Connection = conn;
             conn.Open();
             using (SqlDataReader sdr = cmd.ExecuteReader())
             {
                 while (sdr.Read())
                 {
                     codice.Add(sdr.GetString(0));
                 }
             }
         }
     }
     return codice.ToArray();
 }

but when i type the third letter i got that authentication error.

It seems it's not passing the User ID and Password values, what should i do?