RevMob session start acknoledgement

I want to put RevMob ads into my game. For this I used following website help to move ahead.

RevMob Integration SDK

I have written complete script for it. I want to preload fullscreen ad then I want to show it.
This reason I want to detect session is started and then I want to pass ad request.

Here is my full script :

private static readonly Dictionary<String, String> REVMOB_APP_IDS = new Dictionary<String, String> () {
		{ "Android", "copy your Android RevMob Media ID here"},
		{ "IOS", "copy your Android RevMob Media ID here" }
	private RevMob revmob;
	private RevMobFullscreen fullscreen;

	void Awake ()
		instance = this;
		revmob = RevMob.Start (REVMOB_APP_IDS, "AppController");

	private void RequestRevMobFullScreen ()
		Debug.Log("request revmob full screen method called......");
		fullscreen = revmob.CreateFullscreen ();

	public void ShowRevMobFullScreen ()
		if (fullscreen != null)
			fullscreen.Show ();
			Debug.Log("show revmob full screen method called......");

	#region IRevMobListener implementation
	public void SessionIsStarted ()
		Debug.Log (">>> Session Started");
		RequestRevMobFullScreen ();

	public void UserClosedTheAd (string revMobAdType)
		Debug.Log (">>> AdClosed: " + revMobAdType);
		RequestRevMobFullScreen ();

In above code, SessionIsStarted() method is listener not called any time so my RequestRevMobFullScreen() method was not called.

Basically I just want to preload my ads. If you have any strategy then please suggest it to me.

do you have the IRevMobListener interface implemented.