rpress_is_zip_valid

This filter is applied to use add validate zip code based on country code, it is including three parameters.
$ret -> is a boolean.
$zip -> is an integer.
$country_code -> is a string containing country code.

An example of how you can append is below:

function add_validate_country_code( $ret, $zip = 0, $country_code = ' ' ) {
$country_code = //set country code;
$ret = true;
}
add_filter('rpress_is_zip_valid', 'add_validate_country_code', 10, 3);