POST https://company.sharepoint.com/sites/siteName/_api/web/lists/getbytitle('Employees')/items 403 (FORBIDDEN)

function GetListItemsFromSPList() {
var siteUrl = "https://company.sharepoint.com/sites/siteName/";
$('#listitems').empty();
$.ajax({
    url: siteUrl + "_api/web/lists/getbytitle('Employees')/items/",
    method: "GET",
    headers: { "Accept": "application/json; odata=verbose" },
    success: function (data) {

        var listItems = data.d.results;
        listItems.forEach(function (entry) {
            var node = document.createElement("LI");
            var textnode = document.createTextNode(entry.UserID);
            node.appendChild(textnode);
            document.getElementById("listitems").appendChild(node);
        });
    },
    error: function (data) {
        alert("Error: " + data)
    }
});}

function AddListItem()  {
var siteUrl = "https://company.sharepoint.com/sites/siteName/";
$.ajax
({
    url: siteUrl + "_api/web/lists/GetByTitle('Employees')/items",
    type: "POST",
    data: JSON.stringify
    ({
        __metadata:
            {
                type: "SP.Data.EmployeesListItem"
            },
        UserID: "US-USERID",
        Position: "Position Name"
    }),
    headers:
        {
            "Accept": "application/json;odata=verbose",
            "Content-Type": "application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val(),
            "X-HTTP-Method": "POST"
        },
    success: function(data, status, xhr)
    {
        GetListItemsFromSPList();
    },
    error: function(xhr, status, error)
    {
        alert("Error");
    }
});}