(Input.GetMouseButtonDown(0)) Not working??

I am making my character jump when the phone screen is touched. I have this which should work based on what i have found searching the internet but it doesn’t register the click on a mouse or when i touch on a phone. I have no idea what is wrong, can anyone point me in the right direction.

	public float jumpHeight = 500f;

	void update () {

		if (Input.GetMouseButtonDown(0))
			jump ();
		}


	void jump() {

		Debug.Log("Jump.");
		GetComponent<Rigidbody2D>().AddForce(Vector2.up * jumpHeight);

	}
  }

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