Modal dialog not working (Razor)

Hi,

I am sorry I am totally new at .NET Core 3.1 and razor pages and there seems to be very few information about Core 3.1 and Razor.

I am trying to show a modal dialog through AJAX to add clients, but is not working, all I get is the same form duplicated:

This is my partial view (AddPartial.cshtml):

@page
@model ClienteModel<div class="modalHeader"><div class="modalLogo"><asp:Image runat="server" ImageUrl="~/content/images/modal_logo.png" alt="" Width="24" style="margin-top:8px" /></div><div class="modalTitle">Add new client</div></div><form asp-page-handler="AddPartial"><div class="mppwrapper">

This is my Cliente.cshtml.cs:

public PartialViewResult OnGetAddPartial()
        {
            return new PartialViewResult
            {
                ViewName = "~/core/cliente/AddPartial",
                ViewData = new ViewDataDictionary<Cliente>(ViewData, new Cliente  { })
            };
        }

This is my Cliente.cshtml:

<div id="modal-placeholder"></div><span class="m-nav__link-text" data-toggle="ajax-modal" data-url="@Url.Page("Cliente", "_AddPartial")" id="btnnewcli">Add new</span>$(function () {
                var placeholderElement = $('#modal-placeholder');$('[data-toggle="ajax-modal"]').on('click', function (event) {
                    var url = $(this).data('url');$.get(url).done(function (data) {
                        placeholderElement.html(data);
                        placeholderElement.find('.modal').modal('show');
                    });
                });
            });

This is my model (Cliente.cs):

public class Cliente
    {

        public Int32 Id { get; set; }
        public string name { get; set; }
}

Any ideas what could be wrong?