diff --git a/oda_wd_client/service/resource_management/types.py b/oda_wd_client/service/resource_management/types.py
index 8933c5e..bb325fa 100644
--- a/oda_wd_client/service/resource_management/types.py
+++ b/oda_wd_client/service/resource_management/types.py
@@ -192,7 +192,7 @@ class SupplierInvoice(WorkdayReferenceBaseModel):
     workday_id_type: Literal[
         "Supplier_invoice_Reference_ID"
     ] = "Supplier_invoice_Reference_ID"
-    invoice_number: str
+    invoice_number: str | None
     company: Company
     currency: Currency
     supplier: Supplier
diff --git a/pyproject.toml b/pyproject.toml
index 3042418..27b5a66 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "oda-wd-client"
-version = "0.0.13"
+version = "0.0.14"
 description = "A library for interacting with Workday from Python"
 authors = [
     "Karl Fredrik Haugland <karlfredrik.haugland@oda.com>",