Custom validation on Contact form 7 plugin

Custom validation on Contact form 7 plugin

add_filter( 'wpcf7_validate_text', 'your_validation_filter_func', 10, 2 );
add_filter( 'wpcf7_validate_text*', 'your_validation_filter_func', 10, 2 );

function your_validation_filter_func( $result, $tag ) {
	$type = $tag['type'];
	$name = $tag['name'];

	if ( 'your-id-number-field' == $name ) {
		$the_value = $_POST[$name];

		if ( is_not_valid_against_your_validation( $the_value ) ) {
			$result['valid'] = false;
			$result['reason'][$name] = "Error message here";
		}
	}

	return $result;
}