Drag and Drop. Grid Array to save if something is placed not working. Fix?,Drag and Drop Grid array to save the positions of placed Object not working. Fix?

I' making a drag and drop sysem, where i need to know if somet$$anonymous$$ng is already placed there.

  private static Transform[,] grid = new Transform[width, height];

here i only create an array with the size of the grid

 void AddTorGrid()
     {
         foreach (Transform c$$anonymous$$ldren in transform)
         {
             int roundedX = Mathf.RoundToInt(c$$anonymous$$ldren.transform.position.x);
             int roundedY = Mathf.RoundToInt(c$$anonymous$$ldren.transform.position.y);
 
             grid[roundedX, roundedY] = c$$anonymous$$ldren;
             Debug.Log(roundedX + "," + roundedY);
         }
     }

I call t$$anonymous$$s function when somet$$anonymous$$ng is placed in the grid save it. And let write the position in the Console. To check the postiitons myself

 bool ValidMove()
     {
         foreach (Transform c$$anonymous$$ldren in transform)
         {
             int roundedX = Mathf.RoundToInt(c$$anonymous$$ldren.transform.position.x);
             int roundedY = Mathf.RoundToInt(c$$anonymous$$ldren.transform.position.y);
 
             if (roundedX < 0 || roundedX >= width || roundedY < 0 || roundedY >= height)
             {
                 return false;
             }
 
             //das $$anonymous$$er um zu gucken ob da bereits was ist
             if (grid[roundedX,roundedY] != null)
             {
                 return false;
             }
             
 
             
         }
 
         return true;
     }

here I'm first checking if the dragged object is placed into the grid. And then check the array ist somet$$anonymous$$ng already is in there.

 public void OnEndDrag(PointerEventData eventData)
     {
 
        
         if (!ValidMove())
         {
 
             rectTransform.anchoredPosition = defaultPos;
             rectTransform.localScale = new Vector3(0.56f, 0.56f, 0.56f);
       
         }
 
         if (ValidMove())
         {
       
             
             if (snapToGrid)
             {
                 transform.position = new Vector2(Mathf.RoundToInt(transform.position.x / gridSize) * gridSize, Mathf.RoundToInt(transform.position.y / gridSize) * gridSize);
                 AddTorGrid();
                 
                     
                 
 
             }
         }
 
         
     }

finally i call the functions by the end of the drag. But t$$anonymous$$s s$$anonymous$$t is not workiing i dont know why. i ckecked everyt$$anonymous$$ng 100times. And logically it must work. Everyt$$anonymous$$ng works except that i can place antoher object on the already pplaced object.

I would be happy if someone can help me.