Functional Area Derivation rule not working

Hi Experts

i have followed the below steps in Dev to test the use of functional area concept before transporting to production by the Derivation is no happening to functional area

1- i activated the FIN_UKV scenario for leading ledger

2- Activate the cost of Sales accounting for relevant company code

3- Use T-code FM_Function to create new functional areas

4-Use cost center category to deriving the functional area by assign the cost center category in the cost center master data and define the functional area in cost center category

5- Activate the Derivation substitution rule through OBBZ

Do i missing something ? why its not still not working while posting and invoice from FB60 ..

Regards

Mahmoud El Nady