I aren't able to jump. I find no mistake in the script

Hi guys, I have a little question. I want to make a third person controller. I wrote the script, made a Cinemachine and tried to play the game. I was able to walk, to sprint but i wasn't able to jump more than one time in one game. Can anybody help me? Have I maybe a script mistake Thanks! PS: Sorry for my bad English

using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class ThirdPersonController : MonoBehaviour
 {
     public Camera MyCamera;
     public float Speed = 5f;
     public float SprintSpeed = 8f;
     public float RotationSpeed = 15;
     public float JumpSpeed = 5f;
     CharacterController MyController;
 
     float mDesiredRotation = 0f;
     bool mSprinting = false;
 
     float mSpeedY = 0;
     float mGravity = -9.81f;
 
     bool mJumping = false;
     // Start is called before the first frame update
     
     void Start()
     {
         MyController = GetComponent<CharacterController>();
     }
 
     // Update is called once per frame
     void Update()
     {
         float x = Input.GetAxisRaw("Horizontal");
         float z = Input.GetAxisRaw("Vertical");
         if(Input.GetButtonDown("Jump") && !mJumping)
         {
             mJumping = true;
             
             mSpeedY += JumpSpeed;
         }
 
         if(!MyController.isGrounded)
         {
             mSpeedY += mGravity * Time.deltaTime;
         }
         else if(mSpeedY < 0)
         {
             mSpeedY = 0;
         }
         if(mJumping && mSpeedY < 0)
         {
             RaycastHit hit;
             if(Physics.Raycast(transform.position, Vector3.down, out hit, .5f, LayerMask.GetMask("Default")))
             {
                 mJumping = false;
             }
         }
         mSprinting = Input.GetKey(KeyCode.LeftShift);
         Vector3 movement = new Vector3(x, 0, z).normalized;
 
         Vector3 rotatedMovement = Quaternion.Euler(0, MyCamera.transform.rotation.eulerAngles.y, 0) * movement;
         Vector3 verticalMovement = Vector3.up * mSpeedY;
         MyController.Move((verticalMovement + (rotatedMovement * (mSprinting ? SprintSpeed : Speed))) * Time.deltaTime);
 
         if (rotatedMovement.magnitude > 0)
         {
             mDesiredRotation = Mathf.Atan2(rotatedMovement.x, rotatedMovement.z) * Mathf.Rad2Deg;
         }
         Quaternion currentRotation = transform.rotation;
         Quaternion targetRotation = Quaternion.Euler(0, mDesiredRotation, 0);
         transform.rotation = Quaternion.Lerp(currentRotation, targetRotation, RotationSpeed * Time.deltaTime);
 
     }
 }![alt text][1]