Facebook Native Ad Not Shwoing

i’m Added native ads on app exiting. but i see in few days ads is request ok but ads impression is low! can any one tell me why? i know all user not click back button to exit but if you calculated in 7 days request and impression % is low!

Block: added native ads on app Exiting dialog!

7 days FAN Report:

@medha_ranjan_barman If on back press the ad is loaded, then I must say it’s not a good approach to showing ads. If you are loading the ad on back press, you can instead load the ad on screen initialize and then directly show on back press. will increase the impressions as well

Yes im set it Already LoadsAds in screen1 initialize! and showing ads after back press to dilog. but this happening with me!