Capacity per date

Eighty seats on Friday, forty on Sunday: two numbers, not two events.

In the paid plans Read the manual

A date can hold a different number of people from the rest of the series. Open it and give it its own seat count for the night you open the balcony, or the afternoon you keep small on purpose.

The count belongs to the date, so selling out on Friday says nothing about Sunday. It is one event on your site and in your menus either way.