Negative Lines on an Invoice

An invoice related to sales operations has a positive total. But it is allowed that one or more lines of the invoice has a negative Line Total.

How this is done in Billit:

Quantity is positive
UnitPriceExcl is negative.

This will be converted in e-invoice networks (e.g. Peppol) in the correct way.

Example of a Json body of an Invoice, where line one has negative total and line 2 has a positive total.

{
 "OrderType": "Invoice",
 "OrderDirection": "Income",
 "OrderNumber": "QS-484125Neg",
 "OrderDate": "2025-12-29",
 "ExpiryDate": "2026-01-31",
  "Customer": {
   "Name": "Billit",
   "VATNumber": "BE0563846944",
   "PartyType": "Customer",
   "Addresses": [
        {
        "AddressType": "InvoiceAddress",
        "Name": "Billit",
        "Street": "Oktrooiplein",
        "StreetNumber": "1",
        "City": "Ghent",
        "Box": "301",
        "CountryCode": "BE"
        }  
   ]
   },
 "OrderLines": [
       {
   "Quantity": 10,
   "UnitPriceExcl": 12.0,
   "Reference": "987965",
   "Description": "Testproduct",
   "VATPercentage": 21.0,
   },
     {
   "Quantity": 2,
   "UnitPriceExcl": -5.00,  //Json : unit price must be negative
   "Description": "Voucher",
   "VATPercentage": 21.0
   }
 ]
}

This is how the negative line will appear in the UBL (line 2 is the negative line):