Delegate an event

Hi everyone, I am new at Unity and want to learn the delegate event, but I have a problem. I want when the button has been clicked, it will show some GUI button on it. I already tried the delegate, but the event is not fired (I mean the GUI button is not shown).

Here is the code that I am using:

The code below is to show the GUI button when I run the game.

 public class IItemDatabase : MonoBehaviour
 {
     public delegate void Action(); // Set the event for the button
 
     public static event Action onClicked; // The event for when the button has been clicked
 
     protected virtual void OnGUI()
     {
         // Call the SetStyle method
         SetStyle();
 
         // Set the GUIContent as the tooltip
         GUIContent buttonText = new GUIContent("Open Shop");
 
         // Set the GUIContent as the tooltip
         GUIContent buttonTexts = new GUIContent("Open Inventory");
 
         // This GUILayoutUtility is useful because it is to fit the content
         Rect buttonGUI = GUILayoutUtility.GetRect(buttonText, "Button");
 
         // This GUILayoutUtility is useful because it is to fit the content
         Rect buttonGUIs = GUILayoutUtility.GetRect(buttonTexts, "Button");
 
         // Set where have to the Rect displayed
         buttonGUI.x = 5;
         buttonGUI.y = Screen.height - 25;
 
         // Set where have to the Rect displayed
         buttonGUIs.x = 125;
         buttonGUIs.y = Screen.height - 25;
 
         // If the button has been clicked
 
         if (GUI.Button(buttonGUI, buttonText, style))
         {
             if (onClicked != null)
             {
                 onClicked();
             }
         }
 
         if (GUI.Button(buttonGUIs, buttonTexts, style))
         {
             if (onClicked != null)
             {
                 onClicked();
             }
         }
 
         // End of the clicked button event
     }
 }

And here is the I want it to display when the button has been clicked:

 public class IInventory : MonoBehaviour 
 {
 
     protected virtual void OnEnable()
     {
         IItemDatabase.onClicked += DoGUI;
     }
 
     protected virtual void OnDisable()
     {
         IItemDatabase.onClicked -= DoGUI;
     }
 
     protected virtual void DoGUI()
     {
        Rect slotRect = new Rect(x * 35 + (Screen.width / 3) + 50, y * 35 + (Screen.height / 3) - 10, 30, 30);
                 GUI.Box(slotRect, GUIContent.none);
     }
 }

But when I clicked the button that it suppose to fired the DoGUI() in IInventory class, it does not run the function.

How do I solve this?

Thank you.

Your answer much appreciated!