I'm using recording service with RTI DDS Connext 6.1.2 to capture data of type KeyedString on the same topic name ('MOVEMENT_LINE')
The key is a normal string, and the value is an xml content.
Bellow example of data where some messages are used as responses and others as requests:
[
{
"key": "2b44272e-694c-4666-a3f3-0ad125812042",