Answer For -> How to Reward Player after watching video - admob rewarded video

 using System.Collections;
 using System.Collections.Generic;
 using System;
 using UnityEngine;
 using GoogleMobileAds;
 using GoogleMobileAds.Api;
 
 public class AdmobGetHub : MonoBehaviour
 {  
    
     private RewardBasedVideoAd rewardBasedVideoAd;
     bool rewardPlayer = false;
 
     // Use this for initialization
     void Start()
     {    
 
         this.rewardBasedVideoAd = RewardBasedVideoAd.Instance;
        
         this.LoadRewardBasedAd();
 
         // has rewarded the user.
         this.rewardBasedVideoAd.OnAdRewarded += HandleRewardBasedVideoRewarded;
         
     }
    
     // Update is called once per frame
     void Update()
     {
         if (rewardPlayer == true)
         {
             // do all the actions
             // Reward the player Her <=================
             msg.SetActive(true);
             rewardPlayer = false;  // to make sure this action will happen only once.
         }
     }
     //-------------------------------------------------------------------------------------
     public void LoadRewardBasedAd()
     {
         #if UNITY_EDITOR
                 string adUnitId = "unused";
         #elif UNITY_ANDROID
             string adUnitId = "ca-app-pub-3940256099942544/5224354917";
         #elif UNITY_IPHONE
             string adUnitId = "ca-app-pub-3940256099942544/1712485313";
         #else
             string adUnitId = "unexpected_platform";
         #endif
 
 
         //Production
         AdRequest adRequest = new AdRequest.Builder ().Build ();
 
         //Test
         //AdRequest adRequest = new AdRequest.Builder()
         //.AddTestDevice(AdRequest.TestDeviceSimulator)       // Simulator.
         //.AddTestDevice("c78b1468accb7ee846fa4f8e61bde0ff")  // My test device.
         //.Build();
 
 
         //Load ad
         this.rewardBasedVideoAd.LoadAd(new AdRequest.Builder().Build(), adUnitId);
     }       
     
 
     public void ShowRewardBasedAd()
     {
         if (this.rewardBasedVideoAd.IsLoaded())
         {
             this.rewardBasedVideoAd.Show();
 
         }
         else
         {
             this.LoadRewardBasedAd();
         }
     }          
 
     public void HandleRewardBasedVideoRewarded(object sender, Reward args)
     {
         rewardPlayer = true;
     }
 }