The calendar identifier, or calendar ID, is a unique string that is part of the link used to access the calendar.
Account-based access
If you have account-based access to Teamup, your calendar identifier is the 6 character string after the c/.
Every account-based link to the same calendar has the same calendar ID, even though the account users have different access permissions.
Shareable link access
If you have access via shareable link, the calendar identifier is the 18 character string after the last slash.
The calendar ID in a shareable link is also known as the calendar key. Every shareable link has a unique calendar key, even if the links all access the same calendar.
If the calendar is on a paid subscription plan, the invoice will show a 7 digit Org ID for the calendar.