Unity ads is showing the same ad on every run on Android

My unity version is 5.5 and I have used native Unity Ad support from Services. I have targetted Android and added namespace UnityEngine.Advertisment and code
void ShowAds() { Advertisment.Show;}
with a function call ShowAds() at specific place of my code as directed in documentation but after building it and running on my android device it shows everytime an ad that ask user to install a unity game from playstore. No other ad is displayed excluding this.

If its not a matter then why its occupying so much of space in my mind and is offering resistance​ of being solved…

Hey Sohail buddy I’ve solved this problem myself and that was not of because any regional fill rate of ads inspite test ads were enabled for development and the ads showing previously were prototype ads made by unity itself for testing. Thanks Sohail for replying.