Functional Area mandatory when creating purchase order with item category D - Service

Hello,

when creating a purchase order with item category D, the functional area becomes mandatory and because of that, FMDERIVE cannot work.

Where is the steering for this, I checked ML90 but I don't see any budgetting related fields there, neither in customizing step

Define Screen Layout at Document Level (MM-Purchasing-Purchase Order). The BADI

ME_PROCESS_PO_CUST - FIELDSELECTION_ITEM doesn't contain anything.

Can somebody point where we can turn this off?

kr

Nico