Enabling Process Order API for Referential Return Order with ONLY Secondary Quantity

Primary Quantity = SFT, Secondary Qty= CTN

We create sales order and return by secondary quantity, primary quantity system calculate by conversion. it is working fine from Sales order User interface.

Issue: organization needs to create referential return orders via Process Order API using secondary quantity (CTN) while system automatically calculates primary quantity (SFT). However:

1. API Limitation: EBS standard Process Order API doesn't support partial quantity returns for referential orders
2. Current Behavior: When trying to return 50 CTN via API, system incorrectly takes full reference order quantity (100 CTN) instead
3. Conversion Issue: Using APPS.INV_CONVERT.INV_UM_CONVERT for manual conversion works and sometimes failed to retrieve exactly. SR says it's a private API