Chartboost didCompleteRewardedVideo event not working

Hey guys, I am showing a rewarded video to players in exchange for some coins in the game I am working on and I am trying to find out when the video finished.

I am using this to display the video and it works well:

   if (Chartboost.hasRewardedVideo(CBLocation.Default))
  {               
       Chartboost.showRewardedVideo(CBLocation.Default);                
  }

However this fails to kick off after the video ends:

 void didCompleteRewardedVideo(CBLocation location, int reward)
  {
  }

I am also subscribing to the event like this:

   void OnEnable()
  {
       Chartboost.didCompleteRewardedVideo += didCompleteRewardedVideo;          
  }

All of the above are in the same script.

How can I solve this? I'd very much appreciate your thoughts!

Thanks!