private static function add_to_cart_handler_grouped( $product_id ) {
		$was_added_to_cart = false;
		$added_to_cart     = array();
		$items             = isset( $_REQUEST['quantity'] ) && is_array( $_REQUEST['quantity'] ) ? wp_unslash( $_REQUEST['quantity'] ) : array(); // phpcs:ignore WordPress.Security.NonceVerification.Recommended, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized

		if ( ! empty( $items ) ) {
			$quantity_set = false;

			foreach ( $items as $item => $quantity ) {
				if ( $quantity <= 0 ) {
					continue;
				}
				$quantity_set = true;

				// Add to cart validation.
				$passed_validation = apply_filters( 'woocommerce_add_to_cart_validation', true, $item, $quantity );

				// Suppress total recalculation until finished.
				remove_action( 'woocommerce_add_to_cart', array( WC()->cart, 'calculate_totals' ), 20, 0 );

				if ( $passed_validation && false !== WC()->cart->add_to_cart( $item, $quantity ) ) {
					$was_added_to_cart      = true;
					$added_to_cart[ $item ] = $quantity;
				}

				add_action( 'woocommerce_add_to_cart', array( WC()->cart, 'calculate_totals' ), 20, 0 );
			}

			if ( ! $was_added_to_cart && ! $quantity_set ) {
				wc_add_notice( __( 'Please choose the quantity of items you wish to add to your cart&hellip;', 'woocommerce' ), 'error' );
			} elseif ( $was_added_to_cart ) {
				wc_add_to_cart_message( $added_to_cart );
				WC()->cart->calculate_totals();
				return true;
			}
		} elseif ( $product_id ) {
			/* Link on product archives */
			wc_add_notice( __( 'Please choose a product to add to your cart&hellip;', 'woocommerce' ), 'error' );
		}
		return false;
	}