This is currently my code. The object moves at the desired speed but using rb.velocity = movement * speed if it jump it remains glued to the ground. I can't understand how I can fix things.

private Vector3 movement;
private float speed = 3;
public bool isGrounded;

void Start()
{
  rb = GetComponent();
}

void Update()
{
  float Horizontal = Input.GetAxis("Horizontal");
  float Vertical = Input.GetAxis("Vertical");
  movement = transform.right * Horizontal + transform.forward * Vertical;
  float origMagnitude = movement.magnitude;
  movement.y = 0.0f;
  movement = movement.normalized * origMagnitude;

  if(isGrounded && Input.GetKeyDown(KeyCode.Space))
    rb.AddForce((Vector3.up + movement) * JumpForce, ForceMode.Impulse);

  RaycastHit hit;
  if (Physics.Raycast(transform.position, transform.TransformDirection(Vector3.down), out hit, rayDistance, layer)) 
    isGrounded = true;
  else 
    isGrounded = false;
}

private void FixedUpdate()
{
  rb.velocity = movement * speed;
}