B4000520- Not able to retreive UOM conversion factor

Hi Team,

I am trying to call BSFN B4000520 by passing below parameters like-

F41002 Get Item UoM Conversion

      BC Branch (F4801)(MMCU) -> BF szBranchPlant

      BC Unit of Measure as Input (F4801)(UOM) -> BF szFromUnitOfMeasure

      PO szUnitOfMeasureAsInput_UOM -> BF szToUnitOfMeasure

      RV Quantity Open -> BF mnQuantityToConvert

      "1" -> BF cSuppressErrorMsg

      BC Item Number - Short (F4801)(ITM) -> BF mnShortItemNumber

      RV Quantity Open <- BF mnQuantityConvertedFromtoTo

But how ever, the BSFN is not looking in F41002 table instead looking directly in F41003 and throwing me an error 0269 which is nothing no standard conversion defined in system. Can someone help me in correcting or identifying the correct mapping of fields?