User Playerprefs to save unlocked level

Hi

I am relatively new Unity and coding and am working on my first game and have been stuck on getting my levels menu to stay unlocked with PlayerPrefs for about 3 weeks now and could do with some help, could someone please point me in the right directions as nothing I try seems to work? My level button and Menu scripts are below.

 public class LevelButton : MonoBehaviour
 {
     public LevelSelectMenu menu;
     public Sprite lockSprite;
     public Text levelText;
     private int level = 0;
     private Button button;
     private Image image;
     
     
    void OnEnable()
    {
        button = GetComponent<Button>();
        image = GetComponent<Image>();
    }
    
    public void Setup(int level, bool isUnlock)
    {
        this.level = level;
        levelText.text = level.ToString();
        
        if(isUnlock)
        {
            image.sprite = null;
            button.enabled = true;
            levelText.gameObject.SetActive(true);  
        }
        else
        {
            image.sprite = lockSprite;
            button.enabled = false;
            levelText.gameObject.SetActive(false);
         }
     }
 
     public void OnClick()
     {
         menu.StartLevel(level);
     }
 }    
     
 





 
 public class LevelSelectMenu : MonoBehaviour
 {
     public int totallevel = 0;
     public int unlockedLevel = 1;
     private LevelButton[] levelButtons;
     private int totalPage = 0;
     private int page = 0;
     private int pageItem = 18;
     public GameObject nextButton;
     public GameObject backButton;
     
     void OnEnable()
     {
         levelButtons = GetComponentsInChildren<LevelButton>();
     }     
     // Start is called before the first frame update
     void Start()
     {
       Refresh();  
     }
     
     public void StartLevel(int level)
     {
         //show player a level info or start the level
         
         if(level==unlockedLevel)
         {
             unlockedLevel+=1;
             SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
 
             Refresh();
         }
     }
     public void ClickNext()
     {
         page+=1;
         Refresh();
     }
     
     public void ClickBack()
     { 
        page-=1;
        Refresh();       
     }
     
     public void Refresh()
     {
         totalPage = totallevel / pageItem;
         
         int index = page * pageItem;
         
         for(int i =0;i<levelButtons.Length;i++)
         {    
             int level = index + i + 1;
             
             if (level<=totallevel)
             {
                 levelButtons[i].gameObject.SetActive(true);
                 levelButtons[i].Setup(level, level <= unlockedLevel);
             }
             else
                 levelButtons[i].gameObject.SetActive(false);
             }
             CheckButton();
             }
         
             private void CheckButton()
             {
                 backButton.SetActive(page > 0);
                 nextButton.SetActive(page < totalPage);    
                             
         
     }    
 }