Change Billable status for a Timesheet entry

In Settings > Timesheet, you have Billable option to modify whether task billable or non-billable in Timesheet.
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If the check-box is selected in settings, you can able to modify the task type in time sheet as Billable / Non-billable .
Timesheet Entry Billable
If the check-box is unchecked in settings, you cannot able to modify the task type in time sheet as Billable / Non-billable .
Timesheet Billable Edit