You will need to increase the logging level of in order to see output payload of PI messages in PIMON
Open NWA and goto the JAVA system Properties
Click on the services tab and select XPI Adapter XI
Edit the property xadapter.logger.conf with value MS=3, AM=3
Update the Logging Configuration settings in NWA in order to log output messages as explained above.
After this you will be able to see the output payload in PIMON.