How to implement api calls with out able to track

• We are implementing admob rewarded video ads in our app. When user completely watch that ad we need to give some points or rewards to the user.
• From app side we are getting response from admob if user completely watch or not. When user completely watch an ad, i want to call server for credit some points or rewards to that user.
• For that i am implementing one api call. I am calling that api inside onRewarded(RewardItem rewardItem) working fine.

Here i am facing one problem:

if anyone are able to track that api (api when i call to credit points or rewards to user) they will directly call it with out watching the ad.

What is the best way to implement this.

via Teja Batchu