diff --git a/libPosSystemAPI/DTO/PayItem.cs b/libPosSystemAPI/DTO/PayItem.cs
index b42ab6e..b412a43 100644
--- a/libPosSystemAPI/DTO/PayItem.cs
+++ b/libPosSystemAPI/DTO/PayItem.cs
@@ -6,7 +6,7 @@ namespace fiskaltrust.DevKit.POSSystemAPI.lib.DTO
     public class PayItem
     {
         [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
-        public string ftPayItemId { get; set; } = string.Empty;
+        public string? ftPayItemId { get; set; } = string.Empty;
 
         public string Description { get; set; } = string.Empty;
         public decimal Amount { get; set; }
diff --git a/libPosSystemAPI/DTO/ReceiptRequest.cs b/libPosSystemAPI/DTO/ReceiptRequest.cs
index 12a6d96..a33b458 100644
--- a/libPosSystemAPI/DTO/ReceiptRequest.cs
+++ b/libPosSystemAPI/DTO/ReceiptRequest.cs
@@ -24,6 +24,14 @@ public ReceiptRequest(string cbReceiptReference, ReceiptCaseBuilder buildableRec
         {
             this.cbReceiptReference = cbReceiptReference;
             this.cbChargeItems = cbChargeItems;
+            // verify that empty ftPayItemIDs are null
+            foreach (var payItem in cbPayItems)
+            {
+                if (payItem.ftPayItemId == "")
+                {
+                    payItem.ftPayItemId = null;
+                }
+            }
             this.cbPayItems = cbPayItems;
             this.ftReceiptCase = buildableReceiptCase.Build();
         }