XML Parsing Error: no root element found when passing .ajax to the same page with a value. Asp.net 3.1 MVC

I'm trying to send an ajax request with a value that would populate a dropdown list. But it returns as an error when I'm trying to send it to the same page. I've tried setting up the function as a separate controller but that doesn't work either.

Dropdown box which initiates the ajax.

<select id="SCat_Cat" name="SCat_Cat" asp-for="Cat_Id" asp-items="(SelectList)ViewBag.Cat_ID" class="form-control" onchange="funct()">
                <option value="0">Select</option>
</select>

ajax script

<script type="text/javascript">
    function funct() {
        var catvalue = document.getElementById("SCat_Cat").value;
        alert(catvalue);
        $.ajax(
            {
                type: "POST",
                url: 'Create?CatID=' + catvalue,
                success: function (result) {
                    if (result.success) {
                        document.getElementById("SCat_SCat").innerHTML = result;
                        alert("Good");
                    }
                },
                error: function (req, status, error) {
                    alert("Error");
                }
            });
        return false;   
    }
</script>

Controller code

        public async Task<IActionResult> Create(string CatID)
        {

            ViewBag.Cat_ID = new SelectList(_context.Category, "Cat_ID", "Cat_Name");
            if (CatID == null)
            {    
                ViewBag.SCat_ID = new SelectList("");
            }
            else
            {
                List<SubCategory> AllSubCategories = _context.SubCategory.ToList();
                List<SubCategory> SelectedSubCategories = AllSubCategories.FindAll(a => a.SCat_Cat.Contains(CatID));
                ViewBag.SCat_ID = new SelectList(SelectedSubCategories, "SCat_ID", "SCat_Name");
            }
            var specialists = await userManager.GetUsersInRoleAsync("Specialist");
            ViewBag.Specialist_ID = new SelectList(specialists, "Id", "UserName");
            return Request.IsAjaxRequest() ? (IActionResult)PartialView() : View();
        }

alternative controller code I've tried that handles this separately

    public IActionResult CreatePopulateSCat(string CatID)
    {
        List<SubCategory> AllSubCategories = _context.SubCategory.ToList();
        List<SubCategory> SelectedSubCategories = AllSubCategories.FindAll(a => a.SCat_Cat.Contains(CatID));
        ViewBag.SCat_ID = new SelectList(SelectedSubCategories, "SCat_ID", "SCat_Name");

        return Request.IsAjaxRequest() ? (IActionResult)PartialView("Create") : View();
    }