Index: ssts-invoice/src/main/java/com/forgon/disinfectsystem/invoicemanager/service/InvoiceManagerImpl.java
===================================================================
diff -u -r20300 -r20310
--- ssts-invoice/src/main/java/com/forgon/disinfectsystem/invoicemanager/service/InvoiceManagerImpl.java	(.../InvoiceManagerImpl.java)	(revision 20300)
+++ ssts-invoice/src/main/java/com/forgon/disinfectsystem/invoicemanager/service/InvoiceManagerImpl.java	(.../InvoiceManagerImpl.java)	(revision 20310)
@@ -2199,9 +2199,9 @@
 				Invoice endInvoice = invoiceList.get(invoiceList.size() - 1);
 				if(endInvoice != null && StringUtils.isNotBlank(endInvoice.getSerialNumber())){
 					if(endInvoice.getSerialNumber().length() > 6){
-						writeBackSerialNo += endInvoice.getSerialNumber().substring(6);
+						writeBackSerialNo += "-" + endInvoice.getSerialNumber().substring(6);
 					}else{
-						writeBackSerialNo += endInvoice.getSerialNumber();
+						writeBackSerialNo += "-" + endInvoice.getSerialNumber();
 					}
 				}
 			}