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>;
    
    		}
    	}
    }

line21 obj.AddComponent; → obj.AddComponent();