There’s an option within MEC > Settings to enable booking reminders.
The only instructions I’ve found are below — I cannot find anything further in the MEC support documents. Can you provide additional information to setup booking reminders?
Important Note: Set a cronjob to call /nas/content/live/abead/wp-content/plugins/modern-events-calendar/app/crons/booking-reminder.php file once per day otherwise it won’t send the reminders. Please note that you should call this file only once per day otherwise it may send the reminders multiple times.