How to add more country states in WP ERP

erp-extra-country-states.php

<?php
// use `erp_states` filter hook to add country states
add_filter( 'erp_states', function ( $states ) {

    $states['NL'] = [
        'DR' => 'Drenthe',
        'FL' => 'Flevoland',
        'FR' => 'Fryslân (fy)',
        'GE' => 'Gelderland',
        'GR' => 'Groningen',
        'LI' => 'Limburg',
        'NB' => 'Noord-Brabant',
        'NH' => 'Noord-Holland',
        'OV' => 'Overijssel',
        'UT' => 'Utrecht',
        'ZE' => 'Zeeland',
        'ZH' => 'Zuid-Holland',
    ];

    return $states;

} );