I cant make my character jump ?,Why can't he jump ?

So ı started looking at the tutorials for the c# today (its my first time) and find a 25 min video about how to code movements for my character, everyhing was working until ı added jumping. Well everything is still working but ı cant jump. anyone who knows c# can you say what ı did wrong here? here is the code: public class Playermovementscrip : MonoBehaviour { public CharacterController controller;

 public float speed = 12f;
 public float gravity = -9.81f;
 public float JumpHeight = 3f;

 public Transform groundCheck;
 public float groundDistence = 0.4f;
 public LayerMask groundMask;

 Vector3 velocity;
 bool isGrounded;

 // Update is called once per frame
 void Update()
 {

     isGrounded = Physics.CheckSphere(groundCheck.position, groundDistence, groundMask);
     
     if(isGrounded && velocity.y < 0)
     {
         velocity.y = -2f;
     }

     float x = Input.GetAxis("Horizontal");
     float z = Input.GetAxis("Vertical");

     Vector3 move = transform.right * x + transform.forward * z;

     controller.Move(move * speed * Time.deltaTime);

     if(Input.GetButtonDown("Jump") && isGrounded)
     {
         velocity.y = Mathf.Sqrt(JumpHeight * -2f * gravity);
     }

     velocity.y += gravity * Time.deltaTime;

     controller.Move(velocity * Time.deltaTime);
 }

} I just wanted to make a little game demo for fun but no :/,ı found a 25 min tutorial on youtube for how to apply FPS Controller. everything was working til the last think ı addet (jumping) ı rewire all of the last stuff but no its still not working and ı have no idea why... (its my first day looking at c#. no accualy its my first time looking to coding launguace for gaming and stuff) here is the code:

public class Playermovementscrip : MonoBehaviour { public CharacterController controller;

 public float speed = 12f;
 public float gravity = -9.81f;
 public float JumpHeight = 3f;

 public Transform groundCheck;
 public float groundDistence = 0.4f;
 public LayerMask groundMask;

 Vector3 velocity;
 bool isGrounded;

 // Update is called once per frame
 void Update()
 {

     isGrounded = Physics.CheckSphere(groundCheck.position, groundDistence, groundMask);
     
     if(isGrounded && velocity.y < 0)
     {
         velocity.y = -2f;
     }

     float x = Input.GetAxis("Horizontal");
     float z = Input.GetAxis("Vertical");

     Vector3 move = transform.right * x + transform.forward * z;

     controller.Move(move * speed * Time.deltaTime);

     if(Input.GetButtonDown("Jump") && isGrounded)
     {
         velocity.y = Mathf.Sqrt(JumpHeight * -2f * gravity);
     }

     velocity.y += gravity * Time.deltaTime;

     controller.Move(velocity * Time.deltaTime);
 }

}

as like ı said I have no clue why it isnt working its the same as the code on youtube... (FIRST PERSON MOVEMENT in Unity - FPS Controller/brackeys)