Customizing No-Show Notifications In Online Booking

We setup email notification for no shows. After marking several appointments of the booking page as now shows the notification failed to send. Is there a time frame i.e. 30 days within which you must mark a no show for the email to be sent?

@Michael the No Show trigger will be active within 1 week of the booking end time. Were these bookings you are adjusting further out than this? If not, then I can take a closer look. If you message me with booking ref# (ABCD-EFGH-IJKL) that would be helpful.

Thanks Ben, yes we were marking old bookings as no shows.