You can not mark any goal as a contributor. However, when a milestone is added to a parent goal, the milestone is marked as a contributing goal to the parent goal automatically. A goal that is aligned with your goal can be marked as contributing.
You can not mark any goal as a contributor. However, when a milestone is added to a parent goal, the milestone is marked as a contributing goal to the parent goal automatically. A goal that is aligned with your goal can be marked as contributing.