diff --git a/BTCPayServer.Client/Models/PaymentRequestBaseData.cs b/BTCPayServer.Client/Models/PaymentRequestBaseData.cs
index d425f61d0..8856e57b5 100644
--- a/BTCPayServer.Client/Models/PaymentRequestBaseData.cs
+++ b/BTCPayServer.Client/Models/PaymentRequestBaseData.cs
@@ -37,6 +37,8 @@ namespace BTCPayServer.Client.Models
         public string Title { get; set; }
         public string Description { get; set; }
         public string Email { get; set; }
+        // Allow payment requests to be linked to invoices outside BTCPay Server using Reference Number
+        public string ReferenceNumber { get; set; }
         public bool AllowCustomPaymentAmounts { get; set; }
 
         [JsonConverter(typeof(StringEnumConverter))]
diff --git a/BTCPayServer/Controllers/UIPaymentRequestController.cs b/BTCPayServer/Controllers/UIPaymentRequestController.cs
index 192347685..1ac3663cd 100644
--- a/BTCPayServer/Controllers/UIPaymentRequestController.cs
+++ b/BTCPayServer/Controllers/UIPaymentRequestController.cs
@@ -206,6 +206,7 @@ namespace BTCPayServer.Controllers
             data.Amount = viewModel.Amount;
             data.Currency = viewModel.Currency ?? store.GetStoreBlob().DefaultCurrency;
             data.Expiry = viewModel.ExpiryDate?.ToUniversalTime();
+            blob.ReferenceNumber = viewModel.ReferenceNumber;
             blob.AllowCustomPaymentAmounts = viewModel.AllowCustomPaymentAmounts;
             blob.FormId = viewModel.FormId;
 
diff --git a/BTCPayServer/Models/PaymentRequestViewModels/ListPaymentRequestsViewModel.cs b/BTCPayServer/Models/PaymentRequestViewModels/ListPaymentRequestsViewModel.cs
index c1c000c44..7600af000 100644
--- a/BTCPayServer/Models/PaymentRequestViewModels/ListPaymentRequestsViewModel.cs
+++ b/BTCPayServer/Models/PaymentRequestViewModels/ListPaymentRequestsViewModel.cs
@@ -48,6 +48,7 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
             Description = blob.Description;
             ExpiryDate = data.Expiry?.UtcDateTime;
             Email = blob.Email;
+            ReferenceNumber = blob.ReferenceNumber;
             AllowCustomPaymentAmounts = blob.AllowCustomPaymentAmounts;
             FormResponse = blob.FormResponse is null
                 ? null
@@ -84,6 +85,10 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
         [MailboxAddress]
         public string Email { get; set; }
         
+        [Display(Name = "Reference Number")]
+        [MaxLength(50)]
+        public string ReferenceNumber { get; set; }
+        
         [Display(Name = "Allow payee to create invoices with custom amounts")]
         public bool AllowCustomPaymentAmounts { get; set; }
 
@@ -106,6 +111,7 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
             Description = blob.Description;
             ExpiryDate = data.Expiry?.UtcDateTime;
             Email = blob.Email;
+            ReferenceNumber = blob.ReferenceNumber;
             AllowCustomPaymentAmounts = blob.AllowCustomPaymentAmounts;
             switch (data.Status)
             {
@@ -127,6 +133,7 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
             }
         }
         public StoreBrandingViewModel StoreBranding { get; set; }
+        public string ReferenceNumber { get; set; }
         public bool AllowCustomPaymentAmounts { get; set; }
         public string Email { get; set; }
         public string Status { get; set; }
@@ -147,11 +154,11 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
 #nullable enable
         public class InvoiceList : List<PaymentRequestInvoice>
         {
-            static HashSet<InvoiceState> stateAllowedToDisplay = new HashSet<InvoiceState>
-                {
-                    new InvoiceState(InvoiceStatus.New, InvoiceExceptionStatus.None),
-                    new InvoiceState(InvoiceStatus.New, InvoiceExceptionStatus.PaidPartial),
-                };
+            private static HashSet<InvoiceState> stateAllowedToDisplay =
+            [
+                new(InvoiceStatus.New, InvoiceExceptionStatus.None),
+                new(InvoiceStatus.New, InvoiceExceptionStatus.PaidPartial)
+            ];
             public InvoiceList()
             {
 
@@ -195,7 +202,7 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
 
         public class PaymentRequestInvoicePayment
         {
-            public static List<ViewPaymentRequestViewModel.PaymentRequestInvoicePayment>
+            public static List<PaymentRequestInvoicePayment>
                 GetViewModels(
                 InvoiceEntity invoice,
                 DisplayFormatter displayFormatter,
@@ -215,7 +222,7 @@ namespace BTCPayServer.Models.PaymentRequestViewModels
 
                     string link = paymentMethodId is null ? null : txLinkProvider.GetTransactionLink(paymentMethodId, txId);
 
-                    return new ViewPaymentRequestViewModel.PaymentRequestInvoicePayment
+                    return new PaymentRequestInvoicePayment
                     {
                         Amount = paymentEntity.PaidAmount.Gross,
                         Paid = paymentEntity.InvoicePaidAmount.Net,
diff --git a/BTCPayServer/Views/UIPaymentRequest/EditPaymentRequest.cshtml b/BTCPayServer/Views/UIPaymentRequest/EditPaymentRequest.cshtml
index 0c56a10a7..1cf5fbc20 100644
--- a/BTCPayServer/Views/UIPaymentRequest/EditPaymentRequest.cshtml
+++ b/BTCPayServer/Views/UIPaymentRequest/EditPaymentRequest.cshtml
@@ -82,6 +82,11 @@
                 <label asp-for="AllowCustomPaymentAmounts" class="form-check-label"></label>
                 <span asp-validation-for="AllowCustomPaymentAmounts" class="text-danger"></span>
             </div>
+            <div class="form-group">
+                <label asp-for="ReferenceNumber" class="form-label"></label>
+                <input asp-for="ReferenceNumber" class="form-control" />
+                <span asp-validation-for="ReferenceNumber" class="text-danger"></span>
+            </div>
             <div class="form-group">
                 <label asp-for="ExpiryDate" class="form-label"></label>
                 <div class="input-group ">
diff --git a/BTCPayServer/Views/UIPaymentRequest/GetPaymentRequests.cshtml b/BTCPayServer/Views/UIPaymentRequest/GetPaymentRequests.cshtml
index afdfc41ce..2ca3f637d 100644
--- a/BTCPayServer/Views/UIPaymentRequest/GetPaymentRequests.cshtml
+++ b/BTCPayServer/Views/UIPaymentRequest/GetPaymentRequests.cshtml
@@ -91,6 +91,7 @@
                             </button>
                         </div>
                     </th>
+                    <th text-translate="true">Number</th>
                     <th text-translate="true">Status</th>
                     <th class="amount-col" text-translate="true">Amount</th>
                     <th></th>
@@ -106,6 +107,9 @@
                         <td class="date-col">
                             @(item.ExpiryDate?.ToBrowserDate() ?? new HtmlString("<span class=\"text-muted\">No Expiry</span>"))
                         </td>
+                        <td>
+                            @item.ReferenceNumber
+                        </td>
                         <td>
                             <span class="badge badge-@item.Status.ToLower() status-badge">@item.Status</span>
                         </td>