Task billable box is required to create a timesheet based invoice to customers. When creating a timesheet-based invoice, the approved hours of only billable tasks will show up in the invoice. So, if you issue an invoice to your customers based on task worked hours, tick the Billable box when creating your tasks.
The Billable Task check box is available in Add Task and Edit Task forms.
Created by Aziza Israilova, April 2019