How do I credit back amounts on a service Purchase Order (PO)?

How do I create a credit memo against a service invoice?

First, disable the SAP Business Network transaction rule Allow suppliers to create line-item credit memo and line-item debit memo against service invoices., because service credit memos are not supported in SAP Ariba Procurement solutions.

If the original service invoice is not paid yet, reject or force-reject the original Invoice Reconciliation (IR) document and then force-reject the associated Service Entry Sheet (SES).
Then, create a new SES and invoice for the corrected amounts.

If the invoice is already paid, create a correction SES and invoice that instead.

If your ERP does not support correction SES, or if you use service PO-based invoicing with automatically-generated SES, file an improvement request to include support for service credit memos.

The source of truth for service invoices is the associated SES; therefore, credit memos against service invoices are not supported in SAP Ariba Procurement solutions.

SAP Business Network for Procurement & Supply Chain > Services