Unity 3D AR (Tap and Place Virtual Object)

Unity Engine
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1

I want the script below ideally function like:

  • tap then place ONE duck
  • after that, I tap again show UI

Now it is working on the second point (show UI) but I will still spawn a new duck even there is already one duck.
How should I modify so that user can only tap and place ONE duck?

public GameObject duck;
public GameObject canvas;
public GameObject confirmationUI;
public GameObject inputUI;

private ARRaycastManager aRRaycastManager;
private ARPlaneManager aRPlaneManager;
private bool isDuckSpawned = false;
private GameObject spawnedObject;
private List<ARRaycastHit> hits = new List<ARRaycastHit>();

public LayerMask ignoreARPlaneMask;

private void Awake()
{
    aRRaycastManager = GetComponent<ARRaycastManager>();
    aRPlaneManager = GetComponent<ARPlaneManager>();

    confirmationUI.SetActive(false);
    inputUI.SetActive(false);
}

void Update()
{
    if (Input.GetMouseButtonDown(0))
    {
        Debug.Log("Mouse clicked");

        if (!isDuckSpawned && aRRaycastManager.Raycast(Input.mousePosition, hits, TrackableType.PlaneWithinPolygon))
        {
            Debug.Log("Duck Gonna be Spawned");
            if (hits.Count > 0)
            {
                ARRaycastHit ARhit = hits[0];
                ARPlane plane = aRPlaneManager.GetPlane(ARhit.trackableId);

                if (plane.alignment == PlaneAlignment.HorizontalUp)
                {
                    Debug.Log("Error D");

                    Pose pose = ARhit.pose;
                    if (spawnedObject == null)
                    {
                        Vector3 spawnDuckPosition = new Vector3(pose.position.x, pose.position.y + 0.03f, pose.position.z);
                        spawnedObject = Instantiate(duck, spawnDuckPosition, pose.rotation);
                        Debug.Log("Error C");

                        spawnedObject.tag = "Placed Duck";
                        isDuckSpawned = true;

                        Debug.Log("Duck Spawned!");
                    }
                    else
                    {
                        Debug.Log("Duck already spawned, ignoring new spawn request.");
                    }
                }
            }
        }
        else
        {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;

            Debug.Log("Error A");

            if (Physics.Raycast(ray, out hit, 100, ignoreARPlaneMask))
            {
                Debug.Log("Hit: " + hit.transform.name + " (" + hit.transform.tag + ")");

                Debug.Log("Error B");

                if (hit.collider.CompareTag("Placed Duck"))
                {
                    Debug.Log("Duck clicked - Showing UI");
                    showUI();
                    return;
                }
            }
        }
    }
}