Create & Save custom WP Metabox

/*
    Add the PMPro meta box to a CPT
*/
function hrx_product_meta_wrapper()
{
    //duplicate this row for each CPT
    add_meta_box('pmpro_require_membership', 'Require Membership', 'hrx_pmpro_page_meta', 'product', 'side');
}
function hrx_pmpro_cpt_init()
{
    if (is_admin() && function_exists('pmpro_hasMembershipLevel')){
        add_action('admin_menu', 'hrx_product_meta_wrapper');
         /* Save post meta on the 'save_post' hook. */
        // add_action( 'save_post', 'hrx_save_product_level_meta', 10, 2 );
    }
}
add_action("init", "hrx_pmpro_cpt_init", 20);

function hrx_pmpro_page_meta($post)
{
    global $membership_levels, $post, $wpdb;
    $page_levels = get_post_meta( $post->ID, 'hrx_product_levels', true );
?>
    <ul id="membershipschecklist" class="list:category categorychecklist form-no-clear">
    <?php
    // Add a nonce field so we can check for it later.
    wp_nonce_field( 'global_notice_nonce', 'global_notice_nonce' );
        $in_member_cat = false;
        foreach($membership_levels as $level)
        {
    ?>
        <li id="membership-level-<?php echo $level->id?>">
            <label class="selectit">
                <input id="in-membership-level-<?php echo $level->id?>" type="checkbox" <?php if(in_array($level->id, $page_levels)) { ?>checked="checked"<?php } ?> name="product_levels[]" value="<?php echo $level->id?>" />
                <?php
                    echo $level->name;
                    //Check which categories are protected for this level
                    $protectedcategories = $wpdb->get_col("SELECT category_id FROM $wpdb->pmpro_memberships_categories WHERE membership_id = $level->id");
                    //See if this post is in any of the level's protected categories
                    if(in_category($protectedcategories, $post->id))
                    {
                        $in_member_cat = true;
                        echo ' *';
                    }
                ?>
            </label>
        </li>
    <?php
        }
    ?>
    </ul>
    <?php

        do_action('pmpro_after_require_membership_metabox', $post);
    ?>
<?php
}

/**
 * When the post is saved, saves our custom data.
 *
 * @param int $post_id
 */
function save_global_notice_meta_box_data( $post_id ) {

    // Check if our nonce is set.
    if ( ! isset( $_POST['global_notice_nonce'] ) ) {
        return;
    }

    // Verify that the nonce is valid.
    if ( ! wp_verify_nonce( $_POST['global_notice_nonce'], 'global_notice_nonce' ) ) {
        return;
    }

    // If this is an autosave, our form has not been submitted, so we don't want to do anything.
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return;
    }

    // Check the user's permissions.
    if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {

        if ( ! current_user_can( 'edit_page', $post_id ) ) {
            return;
        }

    }
    else {

        if ( ! current_user_can( 'edit_post', $post_id ) ) {
            return;
        }
    }

    /* OK, it's safe for us to save the data now. */

    // Make sure that it is set.
    if ( ! isset( $_POST['product_levels'] ) ) {
        return;
    }

    // Sanitize user input.
    $my_data = $_POST['product_levels'];

    // Update the meta field in the database.
    update_post_meta( $post_id, 'hrx_product_levels', $my_data );
}

add_action( 'save_post', 'save_global_notice_meta_box_data' );
// Testing POST Data
add_action('wp_head', 'hrx_test_postdata' );
function hrx_test_postdata() {
    if(!is_admin()){
        global $post;
        echo "<pre>";
        print_r(get_post_meta( $post->ID, 'hrx_product_levels'));
        echo "</pre>";
    }
}