Adding CallBack in MaxSDK Interstitial Ads

I have added MaxSDK Interstitial Ads in my game. when it is shown the scene changes and the scene keeps running in the background of the ad. I want that when the user closes the ad the next scene should load. For this I Have tried to add "
MaxSdkCallbacks.Interstitial.OnAdClosed += HandleOnAdClosed;
"
but it shows error that no such call back exists.
So how to implement this. Please help.

I think it is too late but whatever you can find info about the callbacks here -> MaxSdk