Whether it's for polling or for certain actions, a repeated task known as ‘cron’ is necessary, so you need to schedule scripts to run regularly.
You need to schedule the script to run on your server, for example every 10 minutes.
For example, under Linux, edit your crontab and add the following line:
*/10 * * * * php /path_to_whmcs_directory/modules/registrars/dotsoftextension/domainCron.php (CRON_NAME)