of devices doesn’t have any bearing on this. You could be installed on 10,000 devices and if the owners of the devices are not using your app, there won’t be opportunities to generate impressions. An Impression is a completed ad view. Some video vendors count seeing part of the video as a view, others only count it if the full video is watched.
I don’t know if you have included analytics in your app or not, but it’s a good way to have an extra track on what’s going on. Every time you show a Vungle ad, you could generate an event to your analytics engine to track what’s happening. In your listener for Vungle ads, you could generate events that track completed views, cancelled views, network errors etc.
Analytics is an important function that many developers don’t think about or include in their overall success strategy.
Rob