Explanation
Ref:
https://docs.oracle.com/en/cloud/saas/project-portfolio-management/19a/oapex/define-project-management-conf Topic - Microsoft Project Prevalidation: Explained The following table describes Prevalidation rules for tasks and resource assignments.
Level
Rule
Lowest-level tasks
One labor and multiple expense resources are allowed for a lowest-level task. Remove other resources.
Summary tasks
Only one labor resource with zero allocation is allowed for a summary task. Remove all other resources.
Milestone tasks
No subtasks are allowed under milestone tasks. Milestones must be lowest-level tasks.
Milestone tasks
Milestone tasks must have zero duration.
Milestone tasks
Only one labor resource, with zero effort, is allowed for a milestone task. Remove all other resources.
When exporting milestone tasks, ensure that the tasks:
* Are lowest-levels task with zero duration, that is, the same start and finish dates.
* Have only one labor resource assignment with zero effort.
* Have percent work complete values of 0 or 100 percent. Any other values are set to zero before export.