PaymentErrorCallback typedef

Callback invoked when an error occurs during the payment process.

This callback receives a PaymentException containing details about the error:

• PaymentException.message: A human-readable error description
• PaymentException.errorType: The type of error that occurred
• PaymentException.statusCode: HTTP status code (for API errors)
• PaymentException.errorCode: Specific error code from the API

Example:

void onPaymentError(PaymentException error) {
  switch (error.errorType) {
    case PaymentErrorType.network:
      showNetworkErrorDialog(error.message);
      break;
    case PaymentErrorType.invalidOrderId:
      showInvalidOrderDialog(error.message);
      break;
    default:
      showGenericErrorDialog(error.message);
  }
}