Error : Index was out of range.

Hello, I have a little problem. I took a script from a tutorial to make a shop that I modified :

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using TMPro;
 
 public class Shop : MonoBehaviour
 {
     public Inventory inventoryPlayer;
     public CharacterMotor characterMotor;
     public PlayerInventory playerinv;
     public GameObject shopPanel;
     public GameObject contentOfShopPanel;
     public ItemDataBaseList itemDb;
     public GameObject itemSlot;
 
     [Header("ID des items du shop")]
     public int numOfItem;
 
     public List<int> itemId = new List<int>();
 
     private int amountSlots;
     private int slotsChecked;
     private bool transactionDone;
 
     // Tous les paramètres des objets du shop
     public List<Item> theItem = new List<Item>();
 
     public void Start()
     {
         shopPanel = GameObject.Find("Panel - Shop");
         contentOfShopPanel = shopPanel.transform.GetChild(1).GetChild(0).GetChild(0).gameObject;
         characterMotor = GameObject.FindObjectOfType<CharacterMotor>();
         inventoryPlayer = GameObject.Find("Panel - Inventory(Clone)").GetComponent<Inventory>();
         playerinv = GameObject.FindObjectOfType<PlayerInventory>();
 
         shopPanel.SetActive(false);
     }
 
     // Préparer le shop
     public void PrepareShop()
     {
         shopPanel.SetActive(true);
 
         for (int i = 0; i < numOfItem; i++)
         {
             Instantiate(itemSlot, contentOfShopPanel.transform.position, contentOfShopPanel.transform.rotation, contentOfShopPanel.transform);
 
             theItem.Add(itemDb.getItemByID(itemId[i]));
             
             contentOfShopPanel.transform.GetChild(i).GetChild(0).GetComponent<TextMeshProUGUI>().text = theItem[i].itemName.ToString();
             
             contentOfShopPanel.transform.GetChild(i).GetChild(3).GetComponent<TextMeshProUGUI>().text = theItem[i].itemWeight.ToString();
             
             contentOfShopPanel.transform.GetChild(i).GetChild(5).GetComponent<TextMeshProUGUI>().text = theItem[i].itemValue.ToString();
             
             contentOfShopPanel.transform.GetChild(i).GetChild(1).GetChild(0).GetComponent<Image>().sprite = theItem[i].itemIcon;
 
             contentOfShopPanel.transform.GetChild(i).GetComponent<Button>().onClick.AddListener(delegate { BuyItem(theItem[i]); });
         }
     }
 
     // Nettoyer tout le shop
     public void CleanShop()
     {
         theItem.Clear();
 
         foreach (Transform child in contentOfShopPanel.transform)
         {
             Destroy(child.gameObject);
         }
     }
 
     // Acheter un item
     public void BuyItem(Item finalItem) 
     {
         amountSlots = inventoryPlayer.transform.GetChild(1).childCount;
         transactionDone = false;
         slotsChecked = 0;
         
         foreach (Transform child in inventoryPlayer.transform.GetChild(1))
         {
             if (child.childCount == 0)
             {
                 if (playerinv.florins >= finalItem.itemValue)
                 {
                     inventoryPlayer.addItemToInventory(finalItem.itemID);
                     playerinv.florins -= finalItem.itemValue;
                     transactionDone = true;
                     print("Le joueur a acheté l'objet : " + finalItem.itemName);
                     break;
                 }
                 else
                 {
                     print("Transaction refusée, le joueur n'a pas assez d'argent.");
                 }
             }
             slotsChecked++;
         }
 
         if (slotsChecked == amountSlots && transactionDone == false)
         {
             print("Transaction annulée, pas de place dans l'inventaire.");
         }
     }
 
     // Détection d'entrée du joueur
     public void OnTriggerEnter2D(Collider2D other)
     {
         if (other.tag == "Player")
         {
             PrepareShop();
             characterMotor.isInShop = true;
         }
     }
 
     // Détection de sortie du joueur
     public void OnTriggerExit2D(Collider2D other)
     {
         if (other.tag == "Player")
         {
             CleanShop();
 
             shopPanel.SetActive(false);
             characterMotor.isInShop = false;
         }
     }
 }

Everything works perfectly, except the purchase. It's ironic for a shop.

When I press one buttons to buy an item (so launch the "BuyItem" function), an error appears:

The error is on line 59.

 contentOfShopPanel.transform.GetChild(i).GetComponent<Button>().onClick.AddListener(delegate { BuyItem(theItem[i]); });

It should work, I don't understand! Could you help me?

Sorry about my bad English, I'm French. Thank you in advance!