Each sub-calendar in your Teamup calendar has a unique ID. Sometimes this ID is needed to set up an integration via Zapier or other tools.
Here's a way to get the sub-calendar ID:
Open Teamup in a browser.
In the Calendars list, toggle so only one sub-calendar is visible.
Click the blue open icon under the Filter section.
A pop-up dialog will show the calendar url for that filtered view (showing only one sub-calendar. Look for the &calendars= parameter in the link. The number (underlined in red, below) is the ID for the visible sub-calendar.
Calendar administrators can also get calendar's ID in the settings: