When I click [REGISTER APPOINTMENT] on desktop Outlook app, it is not reflected and email with an appointment code is not sent.

If the appointment information ("ACALL Appointment [*****]") is not in the description field after clicking [REGISTER APPOINTMENT], description field may be formatted as "text".

Set the format to "HTML", click [REGISTER APPOINTMENT] and make sure that the appointment information ("ACALL Appointment [*****]") is in the description field.

After saving the appointment, e-mail with an appointment code will be automatically sent to the guest.