Admob reward player after watching video

Dear unity developers,

I have a small problem, I am using Admob for mediating unity ads at the moment (in the future I will use other networks too).

It shows an unity ad, but I want to reward player after he has watched it, but can't find how to do it, I tried

 public void onRewardedVideoStarted()
 {
     //send message to text field
 }
 public void onRewarded()
 {
     //send message to text field
 }

but it didn't do anything, can anyone help me out?

Thanks