The article outlines the steps to mark a calendar as active or inactive in Sync admin.
An active calendar will be available for Non Working periods as well as Tasklines.
An inactive calendar will not be available for new non working periods or tasklines.
FOLLOW STEPS BELOW:
1. Navigate to Sync Admin -> Lookups -> Calendars
2. Right click on the calendar
3. Click to set Active or inactive
4. Click ok
NB. For a quick tutorial watch below