You can place your own log meesage in a microflow for example, or set the loglevel of one of the internal lognodes to trace: https://docs.mendix.com/refguide/logging#3-log-nodes
Alternatively, you could also set log-levels for REST consume and publish to “trace.” – this would show you exactly what is coming in or going out in the logs
Go to the console viewer, select “advanced” – “set log levels”