Mark guests as arrived or absent once your event starts, and see what it changes.
For: Hosts
Once your event starts, its page shows an Attendance panel. Every host of the event can use it; someone who only administers a group the event was posted to can't.
Marking opens at the start time and stays open until 48 hours after the event ends. After that the panel shows the marks and can't be changed.
Mark your guests1.
Open the event from My events.
2.
In Attendance, set each confirmed guest to Arrived, Absent or Not marked. People on the waitlist aren't listed.
3.
You can change a mark while the panel is open.
If you mark nobody, everyone who had a spot counts as completed. A guest marked Absent is told about 10 minutes later, so a quick correction sends nothing. Setting them back to Arrived or Not marked clears the absence. Every mark feeds the guest's reliability, except an absence on a spot the guest got from the waitlist less than 3 hours before the start: that row shows Short notice · absence won't count, and the guest isn't told.
Tip
Forgot? If your event had guests and you haven't marked anyone yourself when it ends, Party Up reminds you while marking is still open.