Resource creation defaulting organization

Hi,

We need to create 3000 user (Resources) to create the salesperson and we are using API. we have four BU and four legal entity.

under resource information organization field is defaulted if we are not passing any information which is not linked to Legal entity or Business unit we have provided under employment information.

In case we are providing Organization field, we are getting below error "You must provide the manager email  or parent organization  for a nonmanager resource with organization membership role. (HZ-120896)"

we are working on Fusion R12 24D version.

Any pointers will be helpful to identify the issue. thanks a lot in advance.