Read Billing data in Output type processing

Hello,

I have a requirement where I need to read Billing Document data during Output type processing in VF01. I get Billing doc. no. as NAST-OBJKY.

I tried to use FM RV_INVOICE_DOCUMENT_READ and also class CL_WCB_BILL_BUFFER_FOR_PPF, but no results.

The Output type is "Special Function" assigned to custom Program/ Routine. In debug, I see only Billing document number, but I require more data like Sales area and Customer number to post Credit Memo Request (VBRK/ VBRP/ VBPA).

Please Help.

Kr,

Maninder