how to restrict user to choose entity when raising Purchase Requisition/Order

Summary:

We have setup in our Oracle ERP Cloud system e.g one Ledger, 4 business Unit and around 10 Primary balancing segments

each primary balancing segment is one legal entity,

When user raise Purchase Requisition in Particular business Unit, we would like to restrict user can only put entity of charge account to certain entities.

e.g when user raise PR in Business Unit A, buyer can only pick 99887 as entity in the charge account.

When user raise PR in Business unit B , buyer can only pick above 4 entity including 99880,99919,60050 and 60008.

Would you please advise possible solution

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