validation required annotation not working when using prevent default

I work on asp.net MVC application I call API using ajax jQuery to prevent change URL after click submit button

from

Resignation/RequesterIndex?filenumber=103085

to

Resignation/RequesterIndex

and call ajax jQuery working success without change URL but on same time validation annotation model state not working .

so How to display validation ?

public class ResignationRequester
{
    [Required]
    [Display(Name = "Dept./ Branch: ")]
    public string Dept { get; set; }

    [Required]
    [Display(Name = "Designation: ")]
    public string Designation { get; set; }

}

controller action

public class ResignationController : Controller
    {


        public ActionResult RequesterIndex(string filenumber)
        {
            
            return View(resignationRequester);
        }
       
       

        public ActionResult RequesterIndex(ResignationRequester resignationRequester)
        {
          
          
                if (ModelState.IsValid)
                {
                    
                  
                    try
                    {
                        Workforce.InsertToReignation(resignationRequester, (string)Session[SessionKeys.Username], (DateTime)Session[SessionKeys.LastWorkingDate], noticeperiod, (int)Session[SessionKeys.UserCode]);
                    }
                    catch (Exception ex)
                    {
                        ViewBag.errorMsg = "Create Not Done Correctly";
                    }
                    Session[SessionKeys.DirectManager] = GetEmployeeName(Convert.ToString(resignationRequester.DirectManager));
                    Session[SessionKeys.LineManager] = GetEmployeeName(Convert.ToString(resignationRequester.LineManager));
                    if (string.IsNullOrEmpty(ViewBag.errorMsg))
                    {
                        ViewBag.successMessage = "Resignation Submission form Created successfully";
                    }

                 
                }
                else
                {
                    var errors = ModelState.Select(x => x.Value.Errors)
                                            .Where(y => y.Count > 0)
                                            .ToList();
                    ViewBag.errorMsg = "Some Required Fields Not Added";
                    goto InvalidModel;
                }
            }
            else
            {
                ViewBag.errorMsg = "No Data For This File No";
            }
        InvalidModel:
            ViewBag.isPostBack = true;
                return View(resignationRequester);
     
     
    }

view ResignationRequester.cshtml

@model HR.WorkforceRequisition.Models.ResignationRequester

@{
    ViewBag.Title = "Requester Index";
}

@using (Html.BeginForm("RequesterIndex", "Resignation", FormMethod.Post, new { enctype = "multipart/form-data", @id = "ResignationApp", style = "padding-top: 50px" }))
{
    @Html.AntiForgeryToken()
    <div class="form-horizontal">
    @if (!string.IsNullOrEmpty(ViewBag.errorMsg))
    {
        <div class="alert alert-danger">
            @ViewBag.errorMsg
        </div>
    }

    @if (!string.IsNullOrEmpty(ViewBag.successMessage))
    {
        <div class="alert alert-success">
            @ViewBag.successMessage
        </div>
    }

    <div class="row">
        <div class="form-group col-md-6 hover">
            <div class="col-md-5">
                @Html.LabelFor(model => model.Dept, htmlAttributes: new { @class = "control-label" })
            </div>

            <div class="col-md-7">
                @Html.EditorFor(model => model.Dept, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Dept, "", new { @class = "text-danger" })
            </div>
        </div>
        <div class="form-group col-md-6 hover">
            <div class="col-md-5">
                @Html.LabelFor(model => model.Designation, htmlAttributes: new { @class = "control-label" })
            </div>

            <div class="col-md-7">
                @Html.EditorFor(model => model.Designation, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Designation, "", new { @class = "text-danger" })
            </div>
        </div>
    </div>

  
    <div class="form-group">
        <div class="col-md-offset-0 col-md-12">
            <input type="submit" value="Submit" class="btn btn-success" />
        </div>
    </div>
</div>
}

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

call jQuery ajax will call action Requester Index on Resignation Controller

$("#ResignationApp").submit(function (e) {
                e.preventDefault(); // Prevent the default form submission

                var formData = $(this).serialize();
                console.log("data is" + formData)
                $.ajax({
                    type: "POST",
                    url: '@Url.Action("RequesterIndex", "Resignation")',
                   data: formData,
                    success: function (response) {
                        $("#successMessage").show();
                    },
                    error: function (error) {
                        console.error(error);
                    }
                });
            });

I do investigation about that and found issue on ajax jQuery call

e.preventDefault();

when remove it validation working but on same time URL will change

so How to make validation working and URL not changed ?

Expected result

when leave department or designation empty then it must display validation required for me

required validation error without change URL

but this not happen

if i remove e.preventdefault from jQuery it will solve issue validation

but on same time URL will change from

Resignation/RequesterIndex?filenumber=103085 to Resignation/RequesterIndex