With Conversion Exit in query script active, the result in Studio is correct. However, using this script in the composer solution does not give the same/correct result.
The new feature is available in 12.1.
Conversion exit is classified as a new feature in the latest Foundation version 12.1.
Solution: As the customer is using Studio 12.1 and Foundation 12.0, this is the reason that is making them unable to use this feature at their end.
We suggested the customer upgrade to 12.1 and as of now, he used some workaround.