After implementing the placements in your app, you can use the Audience Network Requests Debugger tool to verify that Facebook is receiving the requests from your app.
On your actual iOS or Android test device, iOS or Android, navigate in your app to trigger Audience Network ad placements. The ad requests will show up in the tool. Please verify that the requests are sent with the right placement ID, bundle package name, etc.
This requires a physical device and will not work on the iOS simulator or Android emulator
You need to be logged in to the Facebook app on the same test device that you use in order to be monitored by the tool.
If the ad requests doesn't show up in the tool, it means that Facebook is not receiving the requests as expected. You can check the following items to debug: