integrate admob ads and facebook ads to my android app from server using json

looking for integrate admob advertisement ads to my app android from my sever buy using JSON and start making money ? from it ? need to put your unit id (admob) in the sever.. firbase for ex >> why not implemented in normally inside the code source ? OK let's say something happen and admob shutdown and you can't no longer use the same admob so you need to change the unit id of your ads , in normally implementation you need to update your app to change the unite id , but our method you don't need to update the hole code source it's take just few minutes to change just unite id (ads) in your JSON file exited in my sever .