It's unclear which App will trigger BAdI FCO_SRV_COST_RATE_VALIDATION.
SAP S/4HANA Cloud
Reproducing the Issue
See solution part.
The validation will be triggered while maintaining service cost rate with App Manage Cost Rates - Professional Services.
Service Cost Rate Validation, FM, function module, custom fields and logic, custom logic, Accounting Cost Rate , KBA , CO-OM , Overhead Cost Controlling , Problem