Code Snippet 5 - https://solusipress.com/menambahkan-combo-box-bertingkat-pada-contact-form-7/

cf7-chained-select.php

<?php
$page_slug = 'cf7-administrative-data'; 

function wpcf7_enqueue_script() {	
	if( is_page( $page_slug ) ) {    
		wp_register_script( 'yp-administrative', plugin_dir_url( __FILE__ ) . 'chainedselect.js' );	
	}
}
add_action( 'wp_enqueue_scripts', 'wpcf7_enqueue_script' );

function wpcf7_load_javascript() {
	if( is_page( $page_slug ) ) {    		
	    wp_localize_script( 'yp-administrative', 'chainedselect', array(
	        'ajaxurl' => admin_url( 'admin-ajax.php' ),
	        'security' => wp_create_nonce( 'ajax-get-administrative' ),
	    ));
	    wp_enqueue_script( 'yp-administrative' );	    
    }
}
add_action( 'wp_head', 'wpcf7_load_javascript', 999, 1 );