The problem is normally due to the settings of the antispam email manager or the configuration "Do not send voucher by email" in the "Reservations Settings". You can check the section
Facility / Facility / Reservation Settings
If you put the check mark on "Do not send voucher via email" that would be why the email is not sent.
Simply, but more often, the problem is due to human error in deleting emails by mistake or set incorrect addresses for notification.
To make a test and see if it is indeed a problem of spam, you can try setting a different e- mail address for sending notifications to, and see if emails arrive correctly to this new address.
You can set a different Email, or simply add another one (just write it next to the one already set by separating them with a comma, no spaces) in section:
Facility / Facility / Update Facility Info
Please, do these tests ... and if the problem persists, of course, do not hesitate to contact us!