Can't add to cart grouped products

[admin]

I've tried on my wordpress site to group multiple products and I have no idea why but I can't add products on cart.. I've tried to complete all the input for quantity, but nothing.. Any idea? On single product works..

Here is my grouped.php

<?php
/**
 * Grouped product add to cart
 *
 * @author      WooThemes
 * @package     WooCommerce/Templates
 * @version     2.1.7
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly

global $product, $post;

$parent_product_post = $post;

do_action( 'woocommerce_before_add_to_cart_form' ); ?>

<form class="cart" method="post" enctype='multipart/form-data'>
    <div class="group_table">
        <?php
            foreach ( $grouped_products as $product_id ) :
                $product = wc_get_product( $product_id );
                $post    = $product->post;
                setup_postdata( $post );
                ?>
                    <div class="group-row">
                        <div class="quantity-row">
                            <?php if ( $product->is_sold_individually() || ! $product->is_purchasable() ) : ?>
                                <?php woocommerce_template_loop_add_to_cart(); ?>
                            <?php else : ?>
                                <?php
                                    $quantites_required = true;
                                    woocommerce_quantity_input( array( 'input_name' => 'quantity[' . $product_id . ']', 'input_value' => '0' ) );
                                ?>
                            <?php endif; ?>
                        </div>

                        <div class="label">
                            <label>
                                <?php
                                if($product->is_visible()) {
                                    echo '<a href="' . get_permalink() . '">' . get_the_title() . '</a>';
                                } else {
                                    echo get_the_title();
                                }
                                ?>
                            </label>
                        </div>

                        <?php do_action ( 'woocommerce_grouped_product_list_before_price', $product ); ?>

                        <div class="price">
                            <?php
                                echo ''.$product->get_price_html();

                                if ( $availability = $product->get_availability() ) {
                                    $availability_html = empty( $availability['availability'] ) ? '' : '<p class="stock ' . esc_attr( $availability['class'] ) . '">' . esc_html( $availability['availability'] ) . '</p>';
                                    echo apply_filters( 'woocommerce_stock_html', $availability_html, $availability['availability'], $product );
                                }
                            ?>
                        </div>
                    </div>
                <?php
            endforeach;

            // Reset to parent grouped product
            $post    = $parent_product_post;
            $product = wc_get_product( $parent_product_post->ID );
            setup_postdata( $parent_product_post );
        ?>
    </div>
<?php if($product) {?>
    <input type="hidden" name="add-to-cart" value="<?php echo esc_attr( $product->id ); ?>" />

    <?php if ( $quantites_required ) : ?>

        <?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>

        <button type="submit" class="single_add_to_cart_button button alt"><?php echo ''.$product->single_add_to_cart_text(); ?></button>

        <?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>

    <?php endif; ?>
<?php } else { ?>
    <?php 
        $productid = intval( $_POST['data'] );
        $product = get_product( $productid );

    ?>
    <input type="hidden" name="add-to-cart" value="<?php echo esc_attr( $product->id ); ?>" />

    <?php if ( $quantites_required ) : ?>

        <?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>

        <button type="submit" class="single_add_to_cart_button button alt"><?php echo ''.$product->single_add_to_cart_text(); ?></button>

        <?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>

    <?php endif; ?>
<?php }?>
</form>

<?php do_action( 'woocommerce_after_add_to_cart_form' ); ?>

<strong>UPDATE</strong>

Here is the problem fix..

 woocommerce_quantity_input( array( 'input_name' => 'quantity[' . $product_id->get_id() . ']', 'input_value' => '0' ) );

The problem was at quantity.. before on quantity was all object of

$product_id

now is only the id of product, that was the problem..