!! FM for subtotal D in Billing Document

Hi Expert,

I faced one problem about FM subtotal D in Billing Document.

Currently I want use FM 'WB2_CALCULATE_PROFIT94' to calculate subtotal D, but I don't know how to use this FM,

I was entering I_DOC_TYPE = Document category, I_DOCUMENT =Billing document No. and I_ITEM = Billing document Item No, and come out nothing.

Can anyone help to look into it? Is there anything missing?

Regards,

May.