admob ads do not appear on all of my apps

i'm not a developer,but i'm starting to learn a little bit :) i wanted to get into the apps world,but i didn't have the time so the shortest cut was reskin,i watched a course about it reskinned my first source code that i bought from codecanyon anyway my problem is when i use the google test ads they appear on my game on genymotion or my phone,but when i put the ad id that i got from admob,the ads do not appear,i tried another admob account but the same problem i published the game in hop that it is a problem just with my devices but my adsense account shows like 4000 pages views with 0 impressions i also tried 2 other code sources and the same problem can someone help me with this i'll be very grateful thanks :D