Error in AddComponent

Below is my code but cannot figure it out what is the error occurring "Assets/Scripts/Circle.cs(22,49): error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement"

     using UnityEngine;
     using System.Collections;
     
     [RequireComponent(typeof(GFGrid))]
     public class Circle : MonoBehaviour {
     
         private GFGrid levelGrid;
         public GameObject objectToSpawn;
 
         void OnGUI(){
            Vector3 mousePos = Input.mousePosition;
             mousePos.z = 5.0f;
             mousePos = Camera.main.ScreenToWorldPoint(mousePos);
             mousePos.y = 0.4f;
             float top = buttonPosition == ButtonPosition.upLeft ? 0 : Screen.height - 50;
             float left = buttonPosition == ButtonPosition.downRight ? Screen.width - 170 : 0;
             if(GUI.Button(new Rect(left + 10, top - 10, 150, 50), "Try Another Level"))
             {
                 
                 GameObject obj = Instantiate(objectToSpawn, mousePos, Quaternion.identity) as GameObject;
                 obj.AddComponent<GFGrid>;
     
             }
         }
     }