When sharing data between a calling flow and a response flow, how can user context...

https://www.ibm.com/support/knowledgecenter/SSMKHH_10.0.0/com.ibm.etools.mft.doc/cl28163_.html

To store user context data, you can either set a value in the Environment.CallableFlow.UserContext environment variable, or create and populate child folders below it in the message tree. For example, you can use the following command to specify context data to be stored the environment:

SET Environment.CallableFlow.UserContext = 'myData';