Invalid JSON Response - C# MVC

I am currently implementing DataTables and cannot debug this issue I am having. I am trying to use ajax.reload(), and I get Invalid JSON Response. Included below is my code for loading data, which is called after create/update.

function loadData() {
    $.ajax({
        url: "/Home/List",
        type: "GET",
        contentType: "application/json;charset=utf-8",
        dataType: "json",
        success: function (result) {
            var html = '';
            $.each(result, function (key, item) {
                html += '<tr>';
                html += '<td>' + item.itemName + '</td>';
                html += '<td>' + item.itemType + '</td>';
                html += '<td>' + item.itemPurchased + '</td>';
                html += '<td>' + item.itemSKU + '</td>';
                html += '<td>' + item.itemSize + '</td>';
                html += '<td>' + item.itemColor + '</td>';
                html += '<td>' + "$"+ item.itemPrice + '</td>';
                html += '<td>
                            <a href="#" onclick="return getbyID(' + item.itemID + ')">Edit</a> 
                          | <a href="#" onclick="Delete(' + item.itemID + ')">Delete</a> 
                          | <a href="#" onclick="return getsell(' + item.itemID + ')">Sell</a>
                        </td>';
                html += '</tr>';
            });
            $('.tbody').html(html);
            $('#myTBODY').DataTable().ajax.reload(); 
            
        },
        error: function (errormessage) {
            alert(errormessage.responseText);
        }
    });
}

I attempted to check the Network tab on the Chrome Console, and this is what "List" returned:

[
     { 
        "itemID":76,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-03",
         "itemSKU":"F19961",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Blue"
     }, 

     { 
        "itemID":82,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-09",
         "itemSKU":"F19962",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Red"
     }, 

     { 
        "itemID":83,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-09",
         "itemSKU":"F19962",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Red"
     }, 

     { 
        "itemID":84,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-10",
         "itemSKU":"F19961",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Black"
     }, 

     { 
        "itemID":89,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-09",
         "itemSKU":"F19961",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Black"
     }, 

     { 
        "itemID":90,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-09",
         "itemSKU":"F19961",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Black"
     }, 

     { 
        "itemID":91,
         "itemName":"Yeezy Boost 350",
         "itemType":"Shoe",
         "itemPurchased":"2021-02-09",
         "itemSKU":"F19961",
         "itemSize":"5",
         "itemPrice":220,
         "itemColor":"Black"
     } 
 ]

I know that this is a valid JSON, but I just cannot grasp what it is I am doing wrong. I have tried everything on the official DataTables site, and am just stumped. Please let me know if I need to include something else (my List code, my html, etc), and I do apologize if I am not posting this properly.

Edit: Home Controller

public JsonResult List() // lists all inventory
{
    return Json(invDB.ListAll(), JsonRequestBehavior.AllowGet);
}

Edit: ListAll function

public List<Inventory> ListAll()
{
    List<Inventory> lst = new List<Inventory>();
    using (SqlConnection con = new SqlConnection(cd))
    {
        con.Open();
        SqlCommand com = new SqlCommand("SelectItem", con);
        com.CommandType = CommandType.StoredProcedure;
        SqlDataReader rdr = com.ExecuteReader();
        while (rdr.Read())
        {
            lst.Add(new Inventory
            {
                itemID = Convert.ToInt32(rdr["itemID"]),
                itemName = rdr["itemName"].ToString(),
                itemType = rdr["itemType"].ToString(),
                itemPurchased = rdr["itemPurchased"].ToString(),
                itemSKU = rdr["itemSKU"].ToString(),
                itemSize = rdr["itemSize"].ToString(),
                itemColor = rdr["itemColor"].ToString(),
                itemPrice = Convert.ToDouble(rdr["itemPrice"])
            });
        }
        return lst;
    }
}

This is an image of my Network, the "List" returns what I sent above (the JSON I know is valid). I cannot find anything in network that explains the reasoning for invalid data.