multiple autocomplete in aspxtextbox

function OnUserChange(s, e) {
            $(s.GetInputElement()).autocomplete({
                source: function (request, response) {
                    $.ajax({
                        type: 'POST',
                        contentType: "application/json; charset=utf-8",
                        url: global.path + '/Mail/NewMail.aspx/GetUsers',
                        data: "{'keyword':'" + request.term + "'}",
                        dataType: "json",
                        async: false,
                        success: function (data) {
                            data = jQuery.parseJSON(data.d);
                            response($.map(data, function (item) {
                                return {
                                    label: item.FullName,
                                    value: item.FullName,
                                    id: item.UserID
                                }
                            }))
                        }
                    });
                }
            });
        }

<dx:ASPxTextBox ID="txtTo"  runat="server" Width="500px">
       <ClientSideEvents Init="function(s, e) {
        OnUserChange(s, e); 
          }" />
</dx:ASPxTextBox>

[WebMethod]
       public static string GetUsers(string keyword)
       {
           User user = new User();
           string jsonData = JsonConvert.SerializeObject(user.GetAllUsers(keyword));


           return jsonData;


       }