diff --git a/BTCPayServer.Tests/GreenfieldAPITests.cs b/BTCPayServer.Tests/GreenfieldAPITests.cs
index 124acf21a..2da533cbe 100644
--- a/BTCPayServer.Tests/GreenfieldAPITests.cs
+++ b/BTCPayServer.Tests/GreenfieldAPITests.cs
@@ -2247,6 +2247,17 @@ namespace BTCPayServer.Tests
             Assert.Equal("BTC", pp.Currency);
             Assert.True(pp.AutoApproveClaims);
             Assert.Equal(0.79m, pp.Amount);
+
+            // If an invoice doesn't have payment because it has been marked as paid, we should still be able to refund it.
+            invoice = await client.CreateInvoice(user.StoreId, new CreateInvoiceRequest { Amount = 5000.0m, Currency = "USD" });
+            await client.MarkInvoiceStatus(user.StoreId, invoice.Id, new MarkInvoiceStatusRequest { Status = InvoiceStatus.Settled });
+            var refund = await client.RefundInvoice(user.StoreId, invoice.Id, new RefundInvoiceRequest
+            {
+                PaymentMethod = method.PaymentMethodId,
+                RefundVariant = RefundVariant.CurrentRate
+            });
+            Assert.Equal(1.0m, refund.Amount);
+            Assert.Equal("BTC", refund.Currency);
         }
 
         [Fact(Timeout = TestTimeout)]
diff --git a/BTCPayServer/Controllers/GreenField/GreenfieldInvoiceController.cs b/BTCPayServer/Controllers/GreenField/GreenfieldInvoiceController.cs
index ca19fbca1..b66631592 100644
--- a/BTCPayServer/Controllers/GreenField/GreenfieldInvoiceController.cs
+++ b/BTCPayServer/Controllers/GreenField/GreenfieldInvoiceController.cs
@@ -408,10 +408,7 @@ namespace BTCPayServer.Controllers.Greenfield
                 var supported = _payoutHandlers.GetSupportedPayoutMethods(store);
                 if (supported.Contains(payoutMethodId))
                 {
-                    var paymentMethodId = PaymentMethodId.GetSimilarities([payoutMethodId], invoice.GetPayments(false).Select(p => p.PaymentMethodId))
-                        .OrderByDescending(o => o.similarity)
-                        .Select(o => o.b)
-                        .FirstOrDefault();
+                    var paymentMethodId = invoice.GetClosestPaymentMethodId([payoutMethodId]);
                     paymentPrompt = paymentMethodId is null ? null : invoice.GetPaymentPrompt(paymentMethodId);
                 }
             }
@@ -426,6 +423,14 @@ namespace BTCPayServer.Controllers.Greenfield
 
             var accounting = paymentPrompt.Calculate();
             var cryptoPaid = accounting.Paid;
+            var dueAmount = accounting.TotalDue;
+
+            // If no payment, but settled and marked, assume it has been fully paid
+            if (cryptoPaid is 0 && invoice is { Status: InvoiceStatus.Settled, ExceptionStatus: InvoiceExceptionStatus.Marked })
+            {
+                cryptoPaid = accounting.TotalDue;
+                dueAmount = 0;
+            }
             var cdCurrency = _currencyNameTable.GetCurrencyData(invoice.Currency, true);
             var paidCurrency = Math.Round(cryptoPaid * paymentPrompt.Rate, cdCurrency.Divisibility);
             var rateResult = await _rateProvider.FetchRate(
@@ -491,8 +496,6 @@ namespace BTCPayServer.Controllers.Greenfield
                     {
                         return this.CreateValidationError(ModelState);
                     }
-                    
-                    var dueAmount = accounting.TotalDue;
                     createPullPayment.Currency = paymentPrompt.Currency;
                     createPullPayment.Amount = Math.Round(paidAmount - dueAmount, appliedDivisibility);
                     createPullPayment.AutoApproveClaims = true;
diff --git a/BTCPayServer/Controllers/UIInvoiceController.UI.cs b/BTCPayServer/Controllers/UIInvoiceController.UI.cs
index 34b7c1884..08bfb3946 100644
--- a/BTCPayServer/Controllers/UIInvoiceController.UI.cs
+++ b/BTCPayServer/Controllers/UIInvoiceController.UI.cs
@@ -302,12 +302,7 @@ namespace BTCPayServer.Controllers
 
             // Find the most similar payment method to the one used for the invoice
             var defaultRefund =
-                PaymentMethodId.GetSimilarities(
-                    invoice.Payments.Select(o => o.GetPaymentMethodId()),
-                    payoutMethodIds)
-                .OrderByDescending(o => o.similarity)
-                .Select(o => o.b)
-                .FirstOrDefault();
+                invoice.GetClosestPayoutMethodId(payoutMethodIds);
 
             var refund = new RefundModel
             {
@@ -353,11 +348,7 @@ namespace BTCPayServer.Controllers
                 return View("_RefundModal", model);
             }
 
-            var availablePaymentMethodIds = invoice.GetPaymentPrompts().Select(p => p.PaymentMethodId).Where(p => _handlers.Support(p)).ToArray();
-            var paymentMethodId = PaymentMethodId.GetSimilarities([pmi], availablePaymentMethodIds)
-                .OrderByDescending(o => o.similarity)
-                .Select(o => o.b)
-                .FirstOrDefault();
+            var paymentMethodId = invoice.GetClosestPaymentMethodId([pmi]);
 
             var paymentMethod = paymentMethodId is null ? null : invoice.GetPaymentPrompt(paymentMethodId);
             if (paymentMethod?.Currency is null)
@@ -367,8 +358,16 @@ namespace BTCPayServer.Controllers
             }
 
             var accounting = paymentMethod.Calculate();
-            decimal cryptoPaid = accounting.Paid;
-            decimal dueAmount = accounting.TotalDue;
+            var cryptoPaid = accounting.Paid;
+            var dueAmount = accounting.TotalDue;
+
+            // If no payment, but settled and marked, assume it has been fully paid
+            if (cryptoPaid is 0 && invoice is { Status: InvoiceStatus.Settled, ExceptionStatus: InvoiceExceptionStatus.Marked })
+            {
+                cryptoPaid = accounting.TotalDue;
+                dueAmount = 0;
+            }
+
             var paymentMethodCurrency = paymentMethod.Currency;
 
             var isPaidOver = invoice.ExceptionStatus == InvoiceExceptionStatus.PaidOver;
diff --git a/BTCPayServer/Data/InvoiceDataExtensions.cs b/BTCPayServer/Data/InvoiceDataExtensions.cs
index 50d028ca3..f9c0efe41 100644
--- a/BTCPayServer/Data/InvoiceDataExtensions.cs
+++ b/BTCPayServer/Data/InvoiceDataExtensions.cs
@@ -1,6 +1,9 @@
+using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Reflection.Metadata;
+using BTCPayServer.Payments;
+using BTCPayServer.Payouts;
 using BTCPayServer.Services.Invoices;
 using NBitpayClient;
 using Newtonsoft.Json;
@@ -26,6 +29,28 @@ namespace BTCPayServer.Data
             invoiceData.Amount = blob.Price;
             invoiceData.HasTypedBlob<InvoiceEntity>().SetBlob(blob, DefaultSerializer);
         }
+#nullable enable
+        public static PayoutMethodId? GetClosestPayoutMethodId(this InvoiceData invoice, IEnumerable<PayoutMethodId> pmids)
+        {
+            var paymentMethodIds = invoice.Payments.Select(o => o.GetPaymentMethodId()).ToArray();
+            if (paymentMethodIds.Length == 0)
+                paymentMethodIds = invoice.GetBlob().GetPaymentPrompts().Select(p => p.PaymentMethodId).ToArray();
+            return PaymentMethodId.GetSimilarities(pmids, paymentMethodIds)
+                .OrderByDescending(o => o.similarity)
+                .Select(o => o.a)
+                .FirstOrDefault();
+        }
+        public static PaymentMethodId? GetClosestPaymentMethodId(this InvoiceEntity invoice, IEnumerable<PayoutMethodId> pmids)
+        {
+            var paymentMethodIds = invoice.GetPayments(false).Select(o => o.PaymentMethodId).ToArray();
+            if (paymentMethodIds.Length == 0)
+                paymentMethodIds = invoice.GetPaymentPrompts().Select(p => p.PaymentMethodId).ToArray();
+            return PaymentMethodId.GetSimilarities(pmids, paymentMethodIds)
+                .OrderByDescending(o => o.similarity)
+                .Select(o => o.b)
+                .FirstOrDefault();
+        }
+#nullable restore
         public static InvoiceEntity GetBlob(this InvoiceData invoiceData)
         {
 #pragma warning disable CS0618 // Type or member is obsolete