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 true if valid, or onError
with an error code from IapVerificationError on failure.
void ValidatePurchase(Product product, string receipt, Action<bool> onValidated, Action<string> onError)