IVendingMachineView.cs

public interface IVendingMachineView
{
    event EventHandler CoinInserted;
    event EventHandler Cancel;
    event EventHandler Select;
    event EventHandler<NumberEnteredArgs> NumberEntered;

    void ShowMessage(string message);
    void AddProduct(string code, Product p);
}

NumberEnteredArgs.cs

public class NumberEnteredArgs : EventArgs
{
    public int Number { get; }

    public NumberEnteredArgs(int number)
    {
        Number = number;
    }
}

VendingMachinePresenter.cs

public class VendingMachinePresenter
{
    private VendingMachine _vendingMachine;
    private IVendingMachineView _view;

    public VendingMachinePresenter(IVendingMachineView view)
    {
        _view = view;
        _view.Cancel += (sender, e) => _vendingMachine.Cancel(); ;
        _view.Select += (sender, e) => _vendingMachine.Select(); ;
        _view.NumberEntered += OnNumberEntered;
        _view.CoinInserted += OnCoinInserted;

        _vendingMachine = new VendingMachine();
        _vendingMachine.VendingMachineMessage += OnVendingMachineMessage;
        _vendingMachine.ReturningCoins += (sender, e) =>_view.ShowMessage("Returning " + e.Coins + " coins");
        _vendingMachine.SellingProduct += (sender, e) => _view.ShowMessage("Selling " + e.Product.Name);

        AddProducts();
    }

    private void AddProducts()
    {
        foreach (var product in _vendingMachine.Products)
        {
            _view.AddProduct(product.Key, product.Value);
        }
    }

    private void OnNumberEntered(object sender, NumberEnteredArgs e)
    {
        _vendingMachine.EnterNumber(e.Number);
        _view.ShowMessage(string.Join("", _vendingMachine.Numbers));
    }

    private void OnCoinInserted(object sender, EventArgs e)
    {
        _vendingMachine.InsertCoin();
        _view.ShowMessage("You entered " + _vendingMachine.Coins + " coins");
    }

    private void OnVendingMachineMessage(object sender, VendingMachineMessageArgs e)
    {
        switch (e.Message)
        {
            case VendingMachineMessages.NotEnoughCoins:
                _view.ShowMessage("Not enough coins");
                break;
            case VendingMachineMessages.ProductSoldOut:
                _view.ShowMessage("Product sold out");
                break;
            case VendingMachineMessages.InvalidChoice:
                _view.ShowMessage("Invalid choice");
                break;
        }
    }


}

VendingMachineView.cs

public class VendingMachineView : MonoBehaviour, IVendingMachineView
{
    [SerializeField]
    private Text _message;

    [SerializeField]
    private ProductView _productUIPrefab;

    [SerializeField]
    private Transform _productsListUI;

    public event EventHandler CoinInserted;
    public event EventHandler Cancel;
    public event EventHandler Select;
    public event EventHandler<NumberEnteredArgs> NumberEntered;

    private TimedQueue<string> _messageQueue;

    private VendingMachinePresenter _presenter;

    void Start()
    {
        _messageQueue = new TimedQueue<string>(OnMessageDequeued, OnQueueEmpty);

        _presenter= new VendingMachinePresenter(this);
    }
    
    void Update()
        => _messageQueue.Update(Time.deltaTime);

    public void AddProduct(string code, Product product)
        => _productUIPrefab.Create(_productsListUI, code, product);

    public void ShowMessage(string message) 
        => _messageQueue.Enqueue(message);
        


    public void OnCoinButtonClicked()
        => CoinInserted?.Invoke(this, EventArgs.Empty);

    public void OnNumberButtonClicked(int number) 
        => NumberEntered?.Invoke(this, new NumberEnteredArgs(number));

    public void OnSelectButtonClicked() 
        => Select?.Invoke(this,EventArgs.Empty);

    public void OnCancelButtonClicked()
        => Cancel?.Invoke(this, EventArgs.Empty);

    private void OnMessageDequeued(string message)  
        => _message.text = message;

    private void OnQueueEmpty()
        => OnMessageDequeued("Select a product");
}