Dme payment File for invoice & Credit Memo

Dear Sapients,

I have created a DME Tree structure for PAYM. This structure contains header & line items. Header will contain the vendor bank master data inputs & Total payment payable by the bank per vendor for each payment run. The line items contain both invoices & credit memos details & their corresponding amounts.

Issue is getting the total value of all the invoice ➖ credit memo's in the header Field payment.

Currently, it sum-up the values without any sign in the payment file.

Below are the structure screen shots. Really appreciate quick response.

Structure

Header Field payment

Using Aggregation of Ref AMOUNT from line item

Line item reference field Amount

Structure field value of line item payment.

Kindly help to achieve this summation field value for the header.

regards

PBB