Dear Popleys ,
Context variable has 4 different types, including message type and string type.
For string type variable, you can audit it directly ${<variable name>}. For message type, as it's not a string, you cannot use the variable name only. Usually you can use expression ${<variable name>.mainpart} to return the body of the message, which is a string type. For example, ${request.mainpart}, ${<your soap message name>.mainpart}.
for more details about message layer context variables, please refer to,
Message Layer Context Variables - CA API Gateway - 9.3 - CA Technologies Documentation
Regards,
Mark