Soomla In App purchase and onClick.addListener

Hi everyone. I'm trying to implement soomla in app purchase and for linking my PurchaseNoAds function to my No ads Button I used the Onclick.addListener. Now when I click my button it works but it buy the item for 400 times before stopping, and it freeze my pc for a few seconds... Now my question is: where is the problem? In my Onclick.addlistener or in my in app purchase script? thanks for your time. In app purchase script:

 using System;
 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.UI;
 
 namespace Soomla.Store.Example
 {                                                                                                      //Allows for access to Soomla API                                                                              
     public class NoAdsPayment : MonoBehaviour
     {      
         public Button NoAdsButton;
         //Load the Scene with the cube/ setup the soomla intergration
         void Start ()
         {                                                                                                                      
             DontDestroyOnLoad(transform.gameObject);                                                           //Allows this gameObject to remain during level loads, solving restart crashes
             StoreEvents.OnSoomlaStoreInitialized += onSoomlaStoreIntitialized;                                 //Handle the initialization of store events (calls function below - unneeded in this case)
             SoomlaStore.Initialize (new GameAssets());           //Intialize the store
         }
         
         //this is likely unnecessary, but may be required depending on how you plan on doing IAPS
         public void onSoomlaStoreIntitialized(){
         }
 
         void Update()
         {
             if (Application.loadedLevelName == "Menù2") {
                 NoAdsButton = GameObject.Find ("NoADSButton").GetComponent<Button> ();
                 NoAdsButton.onClick.AddListener(() => PurchaseNOADS());
             }
         }            
         //GUI ELEMENTS
         public void PurchaseNOADS() {
             //Button To PURCHASE ITEM
             if (StoreInventory.GetItemBalance("no_ads") == 0)
             {
                 try {
                     Debug.Log("attempt to purchase");
 
                 StoreInventory.BuyItem ("no_ads");
 
                 Debug.Log (StoreInventory.GetItemBalance("no_ads"));          // Print the current status of the IAP
                 if (StoreInventory.GetItemBalance("no_ads") == 1)
                     Debug.Log("EVVIVA");
                 }
                 catch (Exception e)
                 {                                                                                                                                                                               // if the purchase cannot be completed trigger an error message connectivity issue, IAP doesnt exist on ItunesConnect, etc...)
                     Debug.Log ("SOOMLA/UNITY" + e.Message);                                                
                 }
             }
         
         else
         {
                 Debug.Log("Already NOADS");
         }
         }