public function postComboSetToCart() {
        global $wp_query, $usces; // is $wp_query really necessary? who knows...

        // set custom key to `inCart` so we can use Welcart's cart class
        $_POST['inCart'] = $_POST['wcexicsAddToCart'];
        unset($_POST['wcexicsAddToCart']);
        $originalpost = $_POST;

        $ids = array_keys($_POST['inCart']);
        $post_id = (int)$ids[0];
        $skus = array_keys($_POST['inCart'][$post_id]);
        $skucode = urldecode($skus[0]);

        // we need to make sure the item is a combo-set item
        $comboset = ComboSet::getComboSetFromSkuCode($post_id, $skucode);
        if ($comboset instanceof GenericError) {
            PurchaseSanityChecks::exitAddToCartWithError($comboset->message);
        }

        $pvals = self::getAddToCartPostValues($comboset->getId());
        $groupids = $pvals['groupids'];
        $itemoptmap = $pvals['itemoptmap'];

        // save selections in $_SESSION so that they aren't lost in case of an error redirect
        self::setAddToCartSessionVars($comboset->getId(), $groupids, $itemoptmap);

        // check that all group IDs and item IDs exist. Check that required groups have selections
        $error = PurchaseSanityChecks::comboSetSelectionsAreValid($comboset->getId(), $groupids);
        if ($error instanceof GenericError) {
            // abort early since other errors don't matter in this case
            PurchaseSanityChecks::exitAddToCartWithError($error->message);
        }

        // check that the combo-set item division is valid for the group item selections
        $error = PurchaseSanityChecks::comboSetItemDivisionIsValid($comboset->getId(), $groupids);
        if ($error instanceof GenericError) {
            PurchaseSanityChecks::exitAddToCartWithError($error->message);
        }

        // check that item charge types are valid
        $error = PurchaseSanityChecks::comboSetItemChargeTypeIsValid($comboset->getId(), $groupids);
        if ($error instanceof GenericError) {
            PurchaseSanityChecks::exitAddToCartWithError($error->message);
        }

        // get post data for constructing a cart out of the selected group items
        $postdata = self::getInCartPostData($comboset, $groupids, $itemoptmap);

        // use `$usces->incart_check()` to check the combo-set SKU and all selected group items
        self::inCartCheckComboSet($postdata);

        // unset $_SESSION selections since checks passed ($_SESSION['usces_singleitem'] is handled by Welcart)
        $this->unsetSessionVars();

        // Now we need to construct a cart out of all the group items
        $groupitemscart = $this->getGroupItemsCart($postdata)['rawCart'];

        // set $this->payload for use in processing the combo-set item
        $this->payload = [];
        $this->payload['comboSetId'] = $comboset->getId();
        $this->payload['groupItemsCart'] = $groupitemscart;

        // Add the combo-set item to the cart
        add_filter('usces_filter_in_serialize', [$this, 'filterComboSetInSerialize'], 10);
        $_POST = $originalpost;
        $usces->page = 'cart';
        $usces->cart->inCart();
        remove_filter('usces_filter_in_serialize', [$this, 'filterComboSetInSerialize']);

        // let Welcart handle the rest
        add_action('the_post', [$usces, 'action_cartFilter']);
        add_filter('yoast-ga-push-after-pageview', 'usces_trackPageview_cart');
        add_action('template_redirect', [$usces, 'template_redirect']);
    }