Help with jump script

Hi guys. I'm pretty new to Unity and i started to follow some different tutorials to end up with a movement script for my ball and a jump script

I just can't seem to make the jump script work? What am i doing wrong?

Here is a picture of the problem

 using System.Collections;
 
 public class Movement : MonoBehaviour {
 
     public float JumpHeight;
     public float speed;
     
     private Rigidbody rb;
     private float isFalling = false;
     
     void Start ()
     {
         rb = GetComponent<Rigidbody>();
     }
     
     void FixedUpdate ()
     {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = Input.GetAxis ("Vertical");
         
         Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
         
         rb.AddForce (movement * speed);
     
     if (Input.GetKeyDown(KeyCode.Space) && isFalling == false)
     {
         
     GetComponent.<Rigidbody>().velocity.y = JumpHeight;
         isFalling = true;
     }
 }
     
     function OnCollisionStay ()
     {
         isFalling = false;
         
     }
 }