(Level Selection) Only level 1 and 2 is getting unlocked , if i played lvl 2 , lvl 3 is not getting unlocked (i have 7 levels)

So i have 7 levels/scenes . My first level is unlocked and my others not ( thats good) . When i completed level 1 , level 2 is unlocked but when i completed level 2 , level 3 is not unlocked . Can anyone help me please? Script of GameManager :

 using UnityEngine;
 using UnityEngine.SceneManagement;
 
 public class GameManager : MonoBehaviour {
 
     public string nextLevel = "Level2";
     public int levelToUnlock = 2;
 
     public SceneFader sceneFader;
 
     bool gameHasEnded = false;
 
     public float restartDelay = 1f;
 
     public GameObject completeLevelUI;
 
     public void CompleteLevel ()
     {
         completeLevelUI.SetActive(true);
     }
 
     public void EndGame()
     {
         if (gameHasEnded == false)
         {
             gameHasEnded = true;
             Debug.Log("GAME OVER");
             Invoke("Restart", restartDelay);
         }
     
     }
     void Restart()
     {
         SceneManager.LoadScene(SceneManager.GetActiveScene().name);
     }
 
     public void WinLevel ()
     {
         PlayerPrefs.SetInt("levelReached", levelToUnlock);
         sceneFader.FadeTo(nextLevel);
     }
 
 }

Script of EndTrigger (I don't think you need this )

 using UnityEngine;
 
 public class EndTrigger : MonoBehaviour {
 
     public GameManager gameManager;
 
     void OnTriggerEnter ()
     {
         gameManager.WinLevel();
         gameManager.CompleteLevel();
     }
     
    
 }