Hello.
I have a huge experience with Facebook + Instagram marketing.
I have done this a lot of time for many apps and games for iOS, Android as I am the application developer too.
My process is:
1. I first integrate analytics into the app.
2. Then track the audience accordingly and do the required modifications in the promotion.
"I can give you 100% legit audience from the country(s) you select".
And I promise you that you will be 100% satisfied with your work. I have done this a lot of time so I know the promotion strategy specially in the app market.
If you want, I can show you the glimpse of the analytics/promotion I have done before.
For more details, pm me :).