////checkbox ellenorzes
add_action( 'woocommerce_add_to_cart', 'bbloomer_store_gift', 10, 3 );
function bbloomer_store_gift( $cart_item_key, $product_id, $quantity ) {
      $free_product_id = 8692;

      if( isset( $_POST['is-gift'] ) && $_POST['is-gift'] == "igen" && $product_id != $free_product_id ) {
          WC()->cart->add_to_cart( $free_product_id, $quantity );
      }
}