Can't addforce to instantiated object

So I have code that was working over but now does not work. Everytime I click and I have a boolean set to when I pick up ammunition, in this case just a ball, it sets it to true so you can fire. When you fire the AddForce is supposed to fire with variables I have set in the gameObject. I have the ball(Projectile) Set to isKinematic because it errors otherwise.

 public bool hasBall = false;
 private Rigidbody ballInstance;
 public Transform gunTip;
 Rigidbody otherBall;
 public Rigidbody obj;
 public float ballSpeed;
 
 //private bool isAlive = false;

 public AudioClip audioClip;
 AudioSource audioSource;

 void Start()
 {
     audioSource = GetComponent<AudioSource>();
 }

 void FixedUpdate()
 {
     // If the left mouse button is pressed down...
     if (Input.GetMouseButtonDown(0) && GameObject.FindWithTag("Player").GetComponent<PlayerController>().hasBall == true)
     {

         GameObject.FindWithTag("Player").GetComponent<PlayerController>().hasBall = false;
         ballInstance = Instantiate(obj, gunTip.position, gunTip.rotation) as Rigidbody;
         ballInstance.AddForce(gunTip.forward * ballSpeed);

         audioSource.PlayOneShot(audioClip, 0.7f);
     }
 }

}