Task List - Billable Field

In the Task List, double-click the Billable cell for the task whose billable status you want to edit.

A billable task is assumed to be a task that will be billed externally.

The Billable field is only available:

On tasks in workspaces with external billing enabled (external billing is enabled by the PPM administrator at the workspace type level)

and
To users with the workspace-level View Billing Rates permission (project managers by default)

Important: Any changes you make to a task in the Task List are equivalent to editing the task in the Task Details window.

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