Changing Unity Ads Gui Texture

Hello everyone!I just implemented unity ads into my IOS game. It works, so far, but I cannot figure out how to implement a different if statement. Instead of using The standard unity gui ( the translucent gray that is default for script ) I want to use my own 2d texture. The code I have is:

 using System;
 using UnityEngine;
 using UnityEngine.Advertisements;
 
 public class test1 : MonoBehaviour {
     void Awake() {
         if (Advertisement.isSupported) {
             Advertisement.Initialize ("64318");
         } else {
             Debug.Log("Platform not supported");
         }
     }
     
     void OnGUI() {
         if(GUI.Button(new Rect(10, 10, 150, 50), Advertisement.IsReady() ? "Show Ad" : "Waiting...")) {
             // Show with default zone, pause engine and print result to debug log
             Advertisement.Show(null, new ShowOptions {
                 resultCallback = result => {
                     Debug.Log(result.ToString());
                 }
             });
         }
     }
 }

 

I want to use:

 GUI.DrawTexture(new Rect(0, 0, image.width, image.height), image); 

where I define the gui (in the if statement, line 15) however, I have tried implementing it, and no method I use is correct. How would I implement it? Thanks a lot!