diff --git a/pyazul/models/schemas.py b/pyazul/models/schemas.py
index 13a7973..282ba65 100644
--- a/pyazul/models/schemas.py
+++ b/pyazul/models/schemas.py
@@ -68,7 +68,7 @@ def _validate_itbis_field(v: Union[str, int, float, None], info) -> str:
         ValueError: If value is negative or not a valid number
     """
     if v is None:
-        return "0"
+        return "000"
 
     if isinstance(v, float):  # Convert float to int (cents) then to str
         v = str(int(v))
@@ -84,6 +84,9 @@ def _validate_itbis_field(v: Union[str, int, float, None], info) -> str:
     if numeric_val < 0:
         raise ValueError(f"{info.field_name} ('{v}') must be non-negative.")
 
+    if numeric_val == 0:
+        return "000"
+
     return str(numeric_val)
 
 
diff --git a/pyproject.toml b/pyproject.toml
index 7a4f79e..c92e19c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pyazul"
-version = "3.2.0"
+version = "3.2.1"
 description = "An Azul Webservices light wrapper for Python."
 authors = [{ name = "INDEXA Inc.", email = "info@indexa.do" }]
 license = { text = "MIT License" }
diff --git a/tests/e2e/services/test_payment_page_integration.py b/tests/e2e/services/test_payment_page_integration.py
index 9e1b8a4..564a6dd 100644
--- a/tests/e2e/services/test_payment_page_integration.py
+++ b/tests/e2e/services/test_payment_page_integration.py
@@ -38,7 +38,7 @@ def test_valid_amounts(self):
         assert model.ITBIS == "18000"
 
     def test_zero_itbis_format(self):
-        """Test that zero ITBIS is formatted as '0'."""
+        """Test that zero ITBIS is formatted as '000'."""
         model = PaymentPage(
             OrderNumber=generate_order_number(),
             Amount="100000",
@@ -48,7 +48,20 @@ def test_zero_itbis_format(self):
             CancelUrl=HttpUrl("https://example.com/cancel"),
             AltMerchantName=None,
         )
-        assert model.ITBIS == "0"
+        assert model.ITBIS == "000"
+
+    def test_none_itbis_format(self):
+        """Test that none ITBIS is formatted as '000'."""
+        model = PaymentPage(
+            OrderNumber=generate_order_number(),
+            Amount="100000",
+            ITBIS=None,
+            ApprovedUrl=HttpUrl("https://example.com/approved"),
+            DeclineUrl=HttpUrl("https://example.com/declined"),
+            CancelUrl=HttpUrl("https://example.com/cancel"),
+            AltMerchantName=None,
+        )
+        assert model.ITBIS == "000"
 
     def test_invalid_amount_format(self):
         """Test that invalid amount formats are rejected."""