Make sure that at least one rule is configured from the below list:
To control the Packet Monitor action to capture only the packets related to your policy
Navigate to MONITOR | Tools & Monitors > Packet Monitor > General.
Click Monitor Filter tab.
Navigate to Capture Packets tab and click Start Capture.
Packets are not captured until some traffic triggers an App Rules policy (or an Access Rule). You can see the Alert message in the MONITOR | Logs > System Event page when the policy is triggered.
Click Stop Capture after you have captured the desired packets.
You can Export the capture into different formats and look at it in a browser.