Although we have enabled the rule "Allow suppliers to change unit price", it is not possible to change the price on an invoice related to a service PO.
Therefore, we have set PO ControlKey "unitPriceEditable" = yes in cXML, which did not work either.
So, is there any option to manage price differences on service invoices?
A few things to look at
1) Take a look at this link [DSN] Low Cost Service PO - Change/Edit in the Unit Price for Invoice | SAP Community.
2) Another thing to look into is , if you are using Supplier Groups you will have to ensure that the rules are set at the supplier group level as well .
3) Also try setting this rule "Allow suppliers to change the unit price on service sheets"