Ajax request in ASP.NET core razor pages - not updating fields

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Javascript

Ajax

Razor

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(After making changes based on this question I made yesterday)

My goal is to dynamically update two fields every time there's a change made to a dropdown list. In my example, the dropdown is a list of employees, and I need the group/subgroup fields to update every time it changes. I'm attempting to call the C# method I've created which runs 2 linq queries and sets the result to the fields. I've verified that this method works properly.

I now have the following method in my file "Edit.html.cs":

// Updates chosen specialist's group and subgroup
[BindProperty]
public GroupModel Group { get; set; }
public class GroupModel
{
    public string subGroup { get; set; }
    public string group { get; set; }
}
public ActionResult OnPostSearchCurrGroup()
{
    var subgroupQuery = (from c in _context.ppcc_matrix
                         from e in _context.employees
                         from s in _context.subGroups
                         where c.employeesID == e.Id
                         where e.subGroupsID == s.Id
                         select s.subgrp_nm).FirstOrDefault();
    //subGroups.subgrp_nm = subgroupQuery;

    var groupQuery = (from c in _context.ppcc_matrix
                      from e in _context.employees
                      from s in _context.subGroups
                      from g in _context.groups
                      where c.employeesID == e.Id
                      where e.subGroupsID == s.Id
                      where s.groupsID == g.Id
                      select g.grp_nm).FirstOrDefault();
    //groups.grp_nm = groupQuery;

    var result = new GroupModel { subGroup = subgroupQuery, group = groupQuery };
    return new JsonResult(result);
}

I have these three fields in "Edit.cshtml":

<div class="form-group">
    <label asp-for="ppcc_matrix.employeesID" class="control-label"></label>
    <select asp-for="ppcc_matrix.employeesID" class="form-control" id="employee" asp-items="ViewBag.employeesID">
        <option disabled selected value="0" style="display:none">--select--</option>
    </select>
</div>
<div class="form-group">
    <label asp-for="Group.group" id="grptxt">Group</label>
    <input asp-for="Group.group" id="grpnm" class="form-control" disabled />
</div>
<div class="form-group">
    <label asp-for="Group.subGroup" id="subgrptxt">SubGroup</label>
    <input asp-for="Group.subGroup" id="subgrpnm" class="form-control" disabled />
</div>

Using the three id's I've assigned to them, I run this javascript and ajax request in the same file:

@* Dynamically updates the view to show chosen specialist's group and subgroup*@
<script language="javascript" type="text/javascript">
    var employee = document.getElementById('employee');
    employee.addEventListener('change', UpdateGroup);
    function UpdateGroup() {
        $.ajax({
            type: 'post',
            url: '/edit?handler=searchcurrgroup',
            contenttype: "application/json; charset=utf-8",
            datatype: 'json',
            data: '{}',
            async: 'true',
            success: function (data) {
                OnSuccessed(data.subGroup) {
                    document.getElementById('subgrpnm').append(subgroupQuery);
                }
                OnSuccessed(data.group) {
                    document.getElementById('grpnm').append(groupQuery);
                }
            }
        })
    }
</script>

Still, nothing happens and I receive no errors.

What I have tried:

Multiple articles, submitted as a comment on my similar previous question as well.
This article has been helpful, but figuring out how to display the results is confusing to me.