Hi, yes, GTS system can adopt multiple proforma invoice. we add a logic at the beginning of interface function module , if this is first proforma invoice , use the standard logic, otherwise , perform Z logic to update the existing cus dec. This is a big project, need a lot of effort on it.
To stop the 2nd proforma to GTS, Maybe you can add an enhancement in the same place, if this is the 2nd proforma, skip the standard program executing and return. Just my opinion for your referenece.