From 12105ab85c31a6d02f47bd3a8c6c911e48211542 Mon Sep 17 00:00:00 2001
From: Nicolas Dorier <nicolas.dorier@gmail.com>
Date: Tue, 31 Aug 2021 15:08:33 +0900
Subject: [PATCH] Fix rounding error for the first refund option (#2778)
 (#2810)

* Fix rounding error for the first refund option (#2778)

* Fix rounding issue
---
 BTCPayServer/Controllers/InvoiceController.UI.cs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/BTCPayServer/Controllers/InvoiceController.UI.cs b/BTCPayServer/Controllers/InvoiceController.UI.cs
index 796a90d16..5b0e70b26 100644
--- a/BTCPayServer/Controllers/InvoiceController.UI.cs
+++ b/BTCPayServer/Controllers/InvoiceController.UI.cs
@@ -242,10 +242,11 @@ namespace BTCPayServer.Controllers
                     model.RefundStep = RefundSteps.SelectRate;
                     model.Title = "What to refund?";
                     var paymentMethod = invoice.GetPaymentMethods()[paymentMethodId];
+                    var cryptoPaid = paymentMethod.Calculate().Paid.ToDecimal(MoneyUnit.BTC);
                     var paidCurrency =
-                        Math.Round(paymentMethod.Calculate().Paid.ToDecimal(MoneyUnit.BTC) * paymentMethod.Rate,
+                        Math.Round(cryptoPaid * paymentMethod.Rate,
                             cdCurrency.Divisibility);
-                    model.CryptoAmountThen = Math.Round(paidCurrency / paymentMethod.Rate, paymentMethodDivisibility);
+                    model.CryptoAmountThen = cryptoPaid.RoundToSignificant(paymentMethodDivisibility);
                     model.RateThenText =
                         _CurrencyNameTable.DisplayFormatCurrency(model.CryptoAmountThen, paymentMethodId.CryptoCode);
                     rules = store.GetStoreBlob().GetRateRules(_NetworkProvider);