an internal service error during refunding

[talhaiut]

RefundRequest refreq = new RefundRequest()
{
//invoice_number = _useDoc.document,

Internal service error occurring while i was trying to refund.

This is my code snippet for refund.

-------------------------------------------

amount = new Amount()
{
currency = "EUR",
total = pays.AMOUNT
}

};

var payment = Payment.Get(apiContext, pays.PAYID);
var transactionId = payment.transactions[0].related_resources[0].sale.id;
var response = Sale.Refund(apiContext, transactionId, refreq);