I have implemented validation in BAdI, ME_PROCESS_PO_CUST, that in case of service PO(Both create & change) if tax tariff code is empty for a service line, an error will be thrown.
This validation is working fine while creating new service po or doing any change in the existing service line or in case of adding new service line.
But if we make any change in the PO without going to the services tab, then the tax tariff code remains blank in EX_ESLL table which is returned form method, CL_PO_ITEM_HANDLE_MM->IF_SERVICES_MM~GET_SRV_DATA.
I tried implementing the logic in the methods, CHECK, PROCESS_ITEM and PROCESS_HEADER, but faced the same issue.
