Unit cost is not getting populated in Purchase order

1. We are trying to raise a purchase order for an item and the unit cost field in PO detail grid is non-editable. hence it should be autopopulated.

2. The item's primary UOM is in "KG", we are trying to create the purchase order in UOM "LT(Liter)".

3. The unit cost in supplier-item table is defined for UOm - LT(Liter).

4. When we checked, the Unit cost in PO detail creation is auto populated when the UOM in supplier-item price is same as the primary UOM.

5. We have a request to create the PO in a different UOM than the Primary UOM and we have kept the purchasing UOm as LT and the primary UOM is in KG.