Play Game Services plugin Save State Issue

I am using this plugin : https://github.com/playgameservices/play-games-plugin-for-unity

I am trying to save my local user's score to cloud, this is from the original guide :

    using GooglePlayGames;
     using UnityEngine.SocialPlatforms;
     using GooglePlayGames.BasicApi;
     public class MyClass : OnStateLoadedListener {
         void SaveState() {
             // serialize your game state to a byte array:
             byte[] mySaveState = ...;
             int slot = 0; // slot number to use
             ((PlayGamesPlatform) Social.Active).UpdateState(slot,
                 mySaveState, this);
         }
         public void OnStateSaved(bool success, int slot) {
             // handle success or failure
         }
         ...

My user score is an int, so this is what I did

 public void SaveState() {
         // serialize your game state to a byte array: //
         int TheHighScore = PlayerPrefs.GetInt ("highscore");
         byte[] mySaveState = System.BitConverter.GetBytes(TheHighScore);
         int slot = 0; // slot number to use
         ((PlayGamesPlatform)Social.Active).UpdateState(slot,mySaveState,this);
     }
     public void OnStateSaved(bool success, int slot) {
         // handle success or failure
     }

Then the error is :

 error CS1502: The best overloaded method match for `GooglePlayGames.PlayGamesPlatform.UpdateState(int, byte[], GooglePlayGames.BasicApi.OnStateLoadedListener)' has some invalid arguments
 
 error CS1503: Argument `#3' cannot convert `My CS Filename Whatever the name is' expression to type `GooglePlayGames.BasicApi.OnStateLoadedListener'

How to set this up correctly? it is always showing this error "my CS filename Whatever the name is" where ever I put it.

Note : I put this code in a normal CS file :

 using UnityEngine;
 using System.Collections;
 using GooglePlayGames.BasicApi;
 using GooglePlayGames;
 using UnityEngine.SocialPlatforms;
 
 public class blablabla : MonoBehaviour {
  
 bla bla bla ......
 
 }

thx