void OnTriggerEnter2D(Collider2D other)
    {
        if (other.gameObject.CompareTag("PickUp"))
        {
            pickupCount++;
            other.gameObject.SetActive(false);

            // TEST CASE 02
            // Manually generate userId on each pickUp (5 users in total).
            if (Leanplum.HasStarted)
            {
                Dictionary <string, object> attributes = new Dictionary <string, object>();
                attributes.Add("pickUp Count", pickupCount);
                Leanplum.SetUserAttributes(attributes);
                Leanplum.Track("PickUp");

                string userName = "******" + (pickupCount).ToString();
                Leanplum.SetUserId(userName);
                Leanplum.ForceContentUpdate();
            }
        }
    }