Your event is over, but you still have some unpaid orders without vaulted cards. . . Instead of contacting each buyer individually to collect payment, you can use the Self Check-out feature to send these guests an email with an updated message and a link to their account. They can then review their purchases and pay for them online.
If you didn't use the Self Check-out feature during your Gala, you'll need to turn it on and confirm your settings first.