My countdown timer doesn't work,I'm trying to create a countdown timer

I have tried countless time to create a countdown timer form my game, which when reaching zero runs the restart scene. The countdown timer never shows in game or scene view and not sure where I am going wrong. I have place the countdown code into my game manager script and even tried create a new script for this function and pulling as reference in game manager which also didn't work. Not sure what I am doing wrong here, and I have also tried several variations of creating a countdown timer. Any help is greatly appreciate thanks.

I also create an update score method which works perfectly and the score updates in the game, however the countdown timer doesn't show anything.

using System.Collections; using System.Collections.Generic; using UnityEngine; using TMPro; using UnityEngine.SceneManagement; using UnityEngine.UI;

public class GameManagerX : MonoBehaviour { public TextMeshProUGUI scoreText; public TextMeshProUGUI gameOverText; public TextMeshProUGUI timeText; public GameObject titleScreen; public Button restartButton;

 // FIND A WAY TO PULL SCRIPT FROM TIMEX SCRIPT AND ATTACH TO GAME MANAGAER
 //TIME
 public bool timerIsRunning = false;
 public float timeRemaining = 60;

 public List<GameObject> targetPrefabs;   
   

 private int score;
 private float spawnRate = 1.0f;
 public bool isGameActive;

 private float spaceBetweenSquares = 2.5f; 
 private float minValueX = -3.75f; //  x value of the center of the left-most square
 private float minValueY = -3.75f; //  y value of the center of the bottom-most square
 
 // Start the game, remove title screen, reset score, and adjust spawnRate based on difficulty button clicked
 public void StartGame()
 {
     timerIsRunning = true;
     spawnRate /= 5;
     isGameActive = true;
     StartCoroutine(SpawnTarget());
     score = 0;
     UpdateScore(0);
     titleScreen.SetActive(false);
     
     
 }

 private void Update()
 {
     if (timerIsRunning)
     {

         if (timeRemaining > 0)
         {
             timeRemaining -= Time.deltaTime;
             DisplayTime(timeRemaining);
         }

         else
         {
             Debug.Log("Time has run out");
             timeRemaining = 0;
             timerIsRunning = false;

         }
     }

     void DisplayTime(float timeToDisplay)

     {
         float minutes = Mathf.FloorToInt(timeToDisplay / 60);
         float seconds = Mathf.FloorToInt(timeToDisplay % 60);

         timeText.text = string.Format("{0:00}:{1:00}", minutes, seconds);

     }

 }

     // While game is active spawn a random target
     IEnumerator SpawnTarget()
 {
     while (isGameActive)
     {
         yield return new WaitForSeconds(spawnRate);
         int index = Random.Range(0, targetPrefabs.Count);

         if (isGameActive)
         {
             Instantiate(targetPrefabs[index], RandomSpawnPosition(), targetPrefabs[index].transform.rotation);
         }
         
     }

 }

 
   

 // Generate a random spawn position based on a random index from 0 to 3
 Vector3 RandomSpawnPosition()
 {
     float spawnPosX = minValueX + (RandomSquareIndex() * spaceBetweenSquares);
     float spawnPosY = minValueY + (RandomSquareIndex() * spaceBetweenSquares);

     Vector3 spawnPosition = new Vector3(spawnPosX, spawnPosY, 0);
     return spawnPosition;

 }

 // Generates random square index from 0 to 3, which determines which square the target will appear in
 int RandomSquareIndex()
 {
     return Random.Range(0, 4);
 }

 // Update score with value from target clicked
 public void UpdateScore(int scoreToAdd)
 {
     score += scoreToAdd;
     scoreText.text = "score" + score;
 }

 // Stop game, bring up game over text and restart button
 public void GameOver()
 {
     gameOverText.gameObject.SetActive(true);
     restartButton.gameObject.SetActive(true);
     isGameActive = false;
 }

 // Restart game by reloading the scene
 public void RestartGame()
 {
     SceneManager.LoadScene(SceneManager.GetActiveScene().name);
 }

 public void StartGame(int difficulty)
 {
    
     isGameActive = true;
     score = 0;
     spawnRate /= difficulty;

     StartCoroutine(SpawnTarget());
     UpdateScore(0);
     titleScreen.gameObject.SetActive(false);
     

 }

}

,I have made a score update which displays correctly. However I am having trouble doing the same for the countdown timer. It never shows in my scene and I have tried many different variations of could. Could someone please help indicate where I have gone wrong. The timer should countdown from 60 when ended the restart scene should run. I have placed the timer in the game manager script. I create a new script and pull reference, that also didn't work.

using System.Collections; using System.Collections.Generic; using UnityEngine; using TMPro; using UnityEngine.SceneManagement; using UnityEngine.UI;

public class GameManagerX : MonoBehaviour { public TextMeshProUGUI scoreText; public TextMeshProUGUI gameOverText; public TextMeshProUGUI timeText; public GameObject titleScreen; public Button restartButton;

 // FIND A WAY TO PULL SCRIPT FROM TIMEX SCRIPT AND ATTACH TO GAME MANAGAER
 //TIME
 public bool timerIsRunning = false;
 public float timeRemaining = 60;

 public List<GameObject> targetPrefabs;   
   

 private int score;
 private float spawnRate = 1.0f;
 public bool isGameActive;

 private float spaceBetweenSquares = 2.5f; 
 private float minValueX = -3.75f; //  x value of the center of the left-most square
 private float minValueY = -3.75f; //  y value of the center of the bottom-most square
 
 // Start the game, remove title screen, reset score, and adjust spawnRate based on difficulty button clicked
 public void StartGame()
 {
     timerIsRunning = true;
     spawnRate /= 5;
     isGameActive = true;
     StartCoroutine(SpawnTarget());
     score = 0;
     UpdateScore(0);
     titleScreen.SetActive(false);
     
     
 }

 private void Update()
 {
     if (timerIsRunning)
     {

         if (timeRemaining > 0)
         {
             timeRemaining -= Time.deltaTime;
             DisplayTime(timeRemaining);
         }

         else
         {
             Debug.Log("Time has run out");
             timeRemaining = 0;
             timerIsRunning = false;

         }
     }

     void DisplayTime(float timeToDisplay)

     {
         float minutes = Mathf.FloorToInt(timeToDisplay / 60);
         float seconds = Mathf.FloorToInt(timeToDisplay % 60);

         timeText.text = string.Format("{0:00}:{1:00}", minutes, seconds);

     }

 }

     // While game is active spawn a random target
     IEnumerator SpawnTarget()
 {
     while (isGameActive)
     {
         yield return new WaitForSeconds(spawnRate);
         int index = Random.Range(0, targetPrefabs.Count);

         if (isGameActive)
         {
             Instantiate(targetPrefabs[index], RandomSpawnPosition(), targetPrefabs[index].transform.rotation);
         }
         
     }

 }

 
   

 // Generate a random spawn position based on a random index from 0 to 3
 Vector3 RandomSpawnPosition()
 {
     float spawnPosX = minValueX + (RandomSquareIndex() * spaceBetweenSquares);
     float spawnPosY = minValueY + (RandomSquareIndex() * spaceBetweenSquares);

     Vector3 spawnPosition = new Vector3(spawnPosX, spawnPosY, 0);
     return spawnPosition;

 }

 // Generates random square index from 0 to 3, which determines which square the target will appear in
 int RandomSquareIndex()
 {
     return Random.Range(0, 4);
 }

 // Update score with value from target clicked
 public void UpdateScore(int scoreToAdd)
 {
     score += scoreToAdd;
     scoreText.text = "score" + score;
 }

 // Stop game, bring up game over text and restart button
 public void GameOver()
 {
     gameOverText.gameObject.SetActive(true);
     restartButton.gameObject.SetActive(true);
     isGameActive = false;
 }

 // Restart game by reloading the scene
 public void RestartGame()
 {
     SceneManager.LoadScene(SceneManager.GetActiveScene().name);
 }

 public void StartGame(int difficulty)
 {
    
     isGameActive = true;
     score = 0;
     spawnRate /= difficulty;

     StartCoroutine(SpawnTarget());
     UpdateScore(0);
     titleScreen.gameObject.SetActive(false);
     

 }

}