Ref: https://docs.oracle.com/en/cloud/saas/project-portfolio-management/19a/oapex/define-project-management-configuration.html#OAPEX1357147 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.

Ref: https://docs.oracle.com/en/cloud/saas/project-portfolio-management/19a/fapfm/implementing-project-financial-management-applications.html#FAPFM969761 Topic - Entering Planning Resource Breakdown Structure Details Click Navigator > Setup and Maintenance, and search for the Manage Planning and Billing Resource Breakdown Structures task.
Click the Manage Planning and Billing Resource Breakdown Structures link.
Use the Manage Planning and Billing Resource Breakdown Structures page to create new planning resource breakdown structures and to review existing planning and billing resource breakdown structures.
Click the Create icon in the Planning Resource Breakdown Structures section.
Use the Create Planning Resource Breakdown Structure: Basic Information page to provide basic resource breakdown structure information including the name, active dates, and project unit.
Enter a planning resource breakdown structure name and select a date from which the resource breakdown structure is available for use.
Optionally, provide a description and a date to which the planning resource breakdown structure is available for use.
Select a project unit. Only projects created for the selected project unit can use this planning resource breakdown structure.
If you want to allow project managers to add planning resources at the project level, then select the Allow resource changes at project level check box.
Tip: Changes at the project level don't move back to the parent planning resource breakdown structure. Deselect this option to ensure all project using the planning resource breakdown structure use the same resources.
Optionally, select a Job Set as a source of jobs for creating planning resources on your planning resource breakdown structure.
Click Save.

Reference https://docs.oracle.com/en/cloud/saas/project-portfolio-management/19b/oapfm/define-project-organizations.html#OAPFM3094543 Topic - Manage Project Unit Organizations