error 404() when try to make ajax request with type post to function O

Question

I work on asp.net razor , i get error when try make ajax request to access OnPostshiftDataUp

ERROR : Failed to load resource: the server responded with a status of 400 () 

console.log(formdata) // serialize data

serverip=172.16.224.999&printername=Zebra2&Location=SupervisorOffice&__RequestVerificationToken=CfDJ8DvYZnvxyLVKi-zvp3jzTImPtgQsnvTBz4ot8mbln2lEaqGcaT_gzZ-KNNfuEBoqHYSBIdcahXL3LLuum4nfTi2oZDQj-PfodyDAVpa45rYEIb7EcRvHrMn71AyB8PMC6DrqvT8q3cCEcSlt1sYQJ-M

but break point not catch this function meaning not detect there are breakpoint must catch it

the main purpose from ajax request is save data after update data on bootstrap model

what I try for my code

1- function with type post on page model

public ActionResult OnPostshiftDataUp()
        {

            
            return Content("msg");
           
        }

2- ajax request to access function or action OnPostshiftDataUp ajax request i do it

$('#save-btn').click(function () {
                var formData = $('#edit-form').serialize();
                console.log(formData);
            
                $.ajax({
                    url: '?handler=shiftDataUp',
                    
         
                    type: "POST",
                  
                    data: JSON.stringify(formData),
            
                   
                    success: function (result) {
                     
                        $('#edit-modal').modal('hide');
       
                        location.reload();
                    },
                    error: function (xhr, status, error) {
                        console.log(error);
                    }
                });
            });

bootstrap model then send ajax request when click button save

<div class="modal fade" id="editshelflabelModal" tabindex="-1" role="dialog" aria-labelledby="userDetailsModalLabel" aria-hidden="true">
    <div class="modal-dialog modal-dialog-centered" role="document">
        <div class="modal-content">
            <h5 class="modal-title" style="text-align:center;">
                @*<img src="@Url.Content("~/Img/UserProfile1.png")" alt="ImageProfile" style="width:22%;height:10%" />*@

            </h5>
            <div class="modal-header">
                <h5 class="modal-title" id="editshelflabelModaldata" style="margin-left:200px;">Hi,@TempData["UserID"]</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                  <form id="edit-form" method="post">
                  @*  <input type="hidden" id="edit-id" name="ShiftId">*@
                    <div class="form-group">
                        <label for="edit-server">Server IP</label>
                        <input type="text" class="form-control" id="edit-ip" name="serverip">
                    </div>
                    <div class="form-group">
                        <label for="edit-printer">Printer Name</label>
                        <input type="text" class="form-control" id="edit-printername" name="printername">
                    </div>
                    <div class="form-group">
                        <label for="edit-locationsdata">Location Name</label>
                        <input type="text" class="form-control" id="edit-Location" value="save" name="Location">
                    </div>
                </form>
                @*<div class="form-group row">
                    <label for="serverIp" class="col-sm-1 col-form-label" style="font-size:15px;font-family: 'Open Sans', sans-serif;font-weight: bold;">Server IP</label>
                    <div class="col-sm-3">
                        <input id="serverIp" asp-for="User.UserName" readonly type="text" class="form-control" style=" margin-left:10px;font-size:15px;font-family: 'Open Sans' , sans-serif;font-weight: bold;" maxlength="30" />
                    </div>
                </div>
            

            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Close</button>
                <button type="submit" class="btn btn-primary" id="save-btn">Save changes</button>
            </div>
        </div>
    </div>
</div>