When you set up either the Google Calendar or Exchange Calendar integration in Sell (see Integrating your Google Calendar with Sell and Integrating your Exchange Calendar with Sell), you also need to set that external calendar to be the default calendar in Sell.
The default calendar is where all your appointments are stored and if you add or edit an appointment in the Sell calendar, it is synced to the integrated, external calendar. This syncing happens in both directions, so if you add an appointment in, for example, the Google calendar you integrated into Sell, that new appointment will sync with and appear in the Sell calendar as well.
If for some reason you want to add another external Google or Exchange calendar and make it the default calendar in Sell, you can so by updating the Default Calendar setting on the Integrations > Calendars settings page in Sell.
When you change the default calendar, all of the existing appointments in the current default calendar will be copied into the new default calendar. The appointments are not deleted from the current default calendar.
When you add calendars in Sell, they appear in the calendar selection pop-up on the Calendars page.
After you’ve created a new calendar integration and set it as the default calendar in Sell, you can either delete the previous default calendar from Sell on the Integrations > Calendars settings page or you can deselect it in the calendars pop-up.
The current default calendar is at the top of the list of calendars. To deselect a calendar, click the selection circle next to the calendar’s name.