To link an existing task as a subtask, navigate to the Subtasks tab and click the New button and choose Link Tasks. Click on the task from the list of available ones to link, and click Add.
If the task you would like to add is not listed, it may be for the following reasons:
- Marked Complete
- Listed as a Duplicate
Note that if your task does not have a subtask tab, then it is already a subtask to a parent task. The parent task will be listed in the details window, under the Tags.
Users will need view and edit permissions in tasks to perform this action. Depending on the user's project permission settings, they may be able to view all project tasks or just a subset. Watchers specifically added to the task will be able to view it.