Profile notify on submit for event registration additional participants only works if profile is used for primary participant
This one is a little obscure, but thought I might as well note it.
If you set up an event registration using a profile that sends a notification email on submit and you use that profile for the primary participant and the additional participants, everything works as intended. But if the additional participant profile that has the notification is only used for the additional participant and not the primary participant, then no notification will be sent.
This is because we only build the profile fields and send the notification if notify is TRUE for customPre or customPost here.. The notification being sent for the additional participant in the case where the notification profile is used for the primary participant is sort of an unintended side effect and it would be better to handle each profile on the registration form separately.