Method ValidatePurchase
ValidatePurchase(Product, string, Action<bool>, Action<string>)
Validates a purchase asynchronously.
product is the purchased product.
receipt is the raw Unity IAP receipt string (order.Info.Receipt).
Call onValidated with the server's verdict (false means the receipt
was examined and rejected — the purchase is discarded), or onError when
validation could not complete (the purchase stays pending and is retried next launch).
void ValidatePurchase(Product product, string receipt, Action<bool> onValidated, Action<string> onError)