diff --git a/lago_python_client/models/credit_note.py b/lago_python_client/models/credit_note.py
index 6d630c1..3a62049 100644
--- a/lago_python_client/models/credit_note.py
+++ b/lago_python_client/models/credit_note.py
@@ -43,6 +43,7 @@ class CreditNoteResponse(BaseResponseModel):
     number: Optional[str]
     lago_invoice_id: Optional[str]
     invoice_number: Optional[str]
+    purchase_order_number: Optional[str]
     credit_status: Optional[str]
     refund_status: Optional[str]
     reason: Optional[str]
diff --git a/lago_python_client/models/invoice.py b/lago_python_client/models/invoice.py
index 78cc040..b5af3b0 100644
--- a/lago_python_client/models/invoice.py
+++ b/lago_python_client/models/invoice.py
@@ -58,6 +58,7 @@ class OneOffInvoice(BaseModel):
     payment_method: Optional[PaymentMethod]
     invoice_custom_section: Optional[InvoiceCustomSectionInput]
     billing_entity_code: Optional[str]
+    purchase_order_number: Optional[str]
 
 
 class InvoicePreview(BaseModel):
@@ -115,6 +116,7 @@ class InvoiceResponse(BaseResponseModel):
     lago_id: str
     sequential_id: Optional[int]
     number: str
+    purchase_order_number: Optional[str]
     issuing_date: Optional[str]
     payment_dispute_lost_at: Optional[str]
     payment_due_date: Optional[str]
diff --git a/tests/fixtures/invoice.json b/tests/fixtures/invoice.json
index a9720db..72f0ced 100644
--- a/tests/fixtures/invoice.json
+++ b/tests/fixtures/invoice.json
@@ -4,6 +4,7 @@
     "billing_entity_code": "test-company",
     "sequential_id": 15,
     "number": "LAG-1234-001-002",
+    "purchase_order_number": "PO-123",
     "issuing_date": "2022-06-02",
     "payment_due_date": "2022-06-02",
     "payment_overdue": false,
diff --git a/tests/test_invoice_client.py b/tests/test_invoice_client.py
index a3399c7..2cba8cf 100644
--- a/tests/test_invoice_client.py
+++ b/tests/test_invoice_client.py
@@ -170,6 +170,7 @@ def test_valid_find_invoice_request(httpx_mock: HTTPXMock):
     response = client.invoices.find(identifier)
 
     assert response.lago_id == identifier
+    assert response.purchase_order_number == "PO-123"
 
 
 def test_invalid_find_invoice_request(httpx_mock: HTTPXMock):