/**
 * Add the validation messages.
 *
 * This is THE function that is adding the validation messages.
 *
 * @since 1.0.0
 */
function wcasv_add_checkout_validation_messages()
{
    // Check if validation is enabled
    if ('yes' !== get_option('enable_woocommerce_advanced_shipping_validation', 'yes')) {
        return;
    }
    $validation_rules = wcasv_get_validation_posts();
    if ($packages = WC()->shipping->get_packages()) {
        foreach ($packages as $i => $package) {
            foreach ($validation_rules as $post_id) {
                $condition_groups = get_post_meta($post_id, '_conditions', true);
                if (wcasv_match_conditions($condition_groups, $package, $i)) {
                    $message = get_post_meta($post_id, '_message', true);
                    wc_add_notice($message, 'error');
                }
            }
        }
    }
    return;
}
<?php

if (!defined('ABSPATH')) {
    exit;
}
// Exit if accessed directly
$validation_rules = wcasv_get_validation_posts(array('post_status' => array('draft', 'publish')));
?>
<tr valign="top">
	<th scope="row" class="titledesc"><?php 
_e('Shipping validation rules', 'woocommerce-advanced-shipping-validation');
?>
<br />
	</th>
	<td class="forminp">

		<table class='wp-list-table wpc-conditions-post-table widefat'>
			<thead>
				<tr>
					<th style='width: 17px;'></th>
					<th style='padding-left: 10px;'><?php 
_e('Title', 'woocommerce-advanced-shipping-validation');
?>
</th>
					<th style='padding-left: 10px;'><?php 
_e('Message', 'woocommerce-advanced-shipping-validation');
?>
</th>
					<th style='width: 70px;'><?php 
_e('# Groups', 'woocommerce-advanced-shipping-validation');
?>