Ajax Error 400 (Bad Request) Handling in Asp.net core Razor Pages

I have a piece of code that collects the values of the inputs in the HTML page and posts them to a handler using AJAX.

However, when sending by AJAX I get a 400 Bad Request error and the handler is not called.

Where I am going wrong?

$("#sendButton").click(function (event) {
  event.preventDefault();
  var userId = $("#userId").val();
  var userName = $("#username").val();
  var message = $("#message").val();
  var groupId = $("#groupid").val();
  var attachFile = $("#f").get(0).files;

  var formData = new FormData();
  formData.append("FileAttach", attachFile);
  formData.append("UserId", userId);
  formData.append("UserName", userName);
  formData.append("Message", message);
  formData.append("GroupId", groupId);
     
  $.ajax({
    type: "POST",
    url: "Index?handler=SendMessage",
    data: formData,
    encyType: "multipart/form-data",
    processData: false,
    contentType: false
  });

  $("#message").val('').focus();
    const element = document.getElementById("preChat");
    element.scrollIntoView({ block: "end" });
  });

This is handler code

public class InsertChatViewModel
{
  public string UserId { get; set; }
  public string GroupId { get; set; }
  public string Message { get; set; }
  public string UserName { get; set; }
  public IFormFile FileAttach { get; set; }
}

public IActionResult OnPostSendMessage([FromForm] InsertChatViewModel model)
{
  // It is not called here
  return Page();
}

Everything not cheanged when change ajax parameters