Belgium Zip code validation for WooCommerce

functions.php

add_filter('woocommerce_validate_postcode','woo_validate_belgium_postcode',10,3);
 
function woo_validate_belgium_postcode($valid, $postcode, $country){
    if($country=="BE")
            $valid = (bool) preg_match( '/^([0-9]{4})$/', $postcode );
  // Checks your postcode to seee if it matches belgium (4 digits). If not, it will reject validation.
  return $valid;
}