PlayerPrefs Resets Automatically upon returning to the Main Menu

My main menu has the slider. But when i switch to the next scene and return back to the main menu, my PlayerPref value does not work. I want the PlayerPrefs value to be saved when I return back from the next scene. Can someone please help me?

Here is my code on the Main Menu :

  using UnityEngine;
     using UnityEngine.UI;
     
     public class AudioManager : MonoBehaviour
     {
         private static readonly string FirstPlay = "FirstPlay";
         private static readonly string MusicPref = "MusicPref";
         private static readonly string SoundPref = "SoundPref";
         private int firstPlayInt;
         public Slider musicSlider, soundSlider;
         private float musicFloat, soundFloat;
         public AudioSource musicAudio;
         public AudioSource[] soundAudio;
     
         public static AudioManager _instance;
      
         void Start()
         {
             firstPlayInt = PlayerPrefs.GetInt(FirstPlay);
     
             if (firstPlayInt == 0)
             {
                 musicFloat = .125f;
                 soundFloat = .75f;
                 musicSlider.value = musicFloat;
                 soundSlider.value = soundFloat;
                 PlayerPrefs.SetFloat(MusicPref, musicFloat);
                 PlayerPrefs.SetFloat(SoundPref, soundFloat);
                 PlayerPrefs.SetInt(FirstPlay, -1);
             }
             else
             {
                 musicFloat = PlayerPrefs.GetFloat(MusicPref);
                 musicSlider.value = musicFloat;
                 soundFloat = PlayerPrefs.GetFloat(SoundPref);
                 soundSlider.value = soundFloat;
             }
     
         }
     
         public void SaveSoundSettings()
         {
             PlayerPrefs.SetFloat(MusicPref, soundSlider.value);
             PlayerPrefs.SetFloat(SoundPref, soundSlider.value);
         }
     
         void OnApplicationFocus(bool inFocus)
         {
             if (!inFocus)
             {
                 SaveSoundSettings();
             }
             else
             {
                 UpdateSound();
             }
         }
     
         public void UpdateSound()
         {
             musicAudio.volume = musicSlider.value;
     
             for (int i = 0; i < soundAudio.Length; i++)
             {
                 soundAudio[i].volume = soundSlider.value;
             }
         }
     
         void Awake()
          {
              //if we don't have an [_instance] set yet
              if(!_instance)
                  _instance = this ;
              //otherwise, if we do, kill this thing
              else
                  Destroy(this.gameObject) ;
              DontDestroyOnLoad(this.gameObject) ;
          }
     
     }  

and this my code for the next scene:

 using UnityEngine;
 
 public class AudioSetting : MonoBehaviour
 {
 
     private static readonly string MusicPref = "MusicPref";
     private static readonly string SoundPref = "SoundPref";
     private float musicFloat, soundFloat;
     public AudioSource musicAudio;
     public AudioSource[] soundAudio;
 
     void Awake()
     {
         musicFloat = PlayerPrefs.GetFloat(MusicPref);
         soundFloat = PlayerPrefs.GetFloat(SoundPref);
 
         musicAudio.volume = musicFloat;
 
         for (int i = 0; i < soundAudio.Length; i++)
         {
             soundAudio[i].volume = soundFloat;
         }
     }
 
 }