diff --git a/buckaroo/builders/payments/in3_builder.py b/buckaroo/builders/payments/in3_builder.py
index 71e5dab..373d6b5 100644
--- a/buckaroo/builders/payments/in3_builder.py
+++ b/buckaroo/builders/payments/in3_builder.py
@@ -25,6 +25,13 @@ def get_allowed_service_parameters(self, action: str = "Pay") -> Dict[str, Any]:
                     "description": "Shipping customer information",
                 },
                 "article": {"type": list, "required": True, "description": "IN3 articles"},
+                "route": {
+                    "type": str,
+                    "required": False,
+                    "description": (
+                        "In3 acquirer route, e.g. 'abn_b2b' for ABN-AMRO Achteraf Betalen"
+                    ),
+                },
             }
 
         return {}
diff --git a/examples/abn_amro_achteraf_betalen.py b/examples/abn_amro_achteraf_betalen.py
new file mode 100644
index 0000000..5f38bc0
--- /dev/null
+++ b/examples/abn_amro_achteraf_betalen.py
@@ -0,0 +1,97 @@
+#!/usr/bin/env python3
+"""Demo of ABN-AMRO Achteraf Betalen via the In3 payment method.
+
+Same underlying service as In3 V3 — setting the optional ``Route`` service
+parameter to ``abn_b2b`` selects ABN-AMRO Achteraf Betalen instead of the
+default In3 acquirer. NL/B2B only. Gated on ``BUCKAROO_STORE_KEY`` /
+``BUCKAROO_SECRET_KEY`` env vars.
+"""
+
+import os
+import sys
+
+# Add parent directory to Python path so the demo can import the SDK in-place.
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+
+from buckaroo.app import Buckaroo
+
+
+def _have_credentials() -> bool:
+    if not os.getenv("BUCKAROO_STORE_KEY") or not os.getenv("BUCKAROO_SECRET_KEY"):
+        print("⚠️  Set BUCKAROO_STORE_KEY and BUCKAROO_SECRET_KEY to run this demo")
+        return False
+    return True
+
+
+def demo_abn_amro_achteraf_betalen() -> None:
+    """Pay via In3 with the ABN-AMRO Achteraf Betalen route."""
+    print("\nABN-AMRO Achteraf Betalen (In3, Route=abn_b2b)")
+    print("-" * 40)
+    if not _have_credentials():
+        return
+
+    try:
+        app = Buckaroo.from_env()
+
+        # create_payment(method, params) dispatches through the PaymentMethodFactory
+        # and returns a ready-to-execute In3Builder.
+        builder = app.payments.create_payment(
+            "in3",
+            {
+                "currency": "EUR",
+                "amount": 121.00,
+                "description": "ABN-AMRO Achteraf Betalen demo",
+                "invoice": "ABN-B2B-DEMO-001",
+                "return_url": "https://www.buckaroo.nl",
+                "return_url_cancel": "https://www.buckaroo.nl/cancel",
+                "return_url_error": "https://www.buckaroo.nl/error",
+                "return_url_reject": "https://www.buckaroo.nl/reject",
+                "service_parameters": {
+                    "billingCustomer": [
+                        {
+                            "firstName": "John",
+                            "lastName": "Doe",
+                            "chamberOfCommerce": "12345678",
+                            "companyName": "Acme B.V.",
+                        }
+                    ],
+                    "shippingCustomer": [
+                        {
+                            "firstName": "John",
+                            "lastName": "Doe",
+                            "chamberOfCommerce": "12345678",
+                            "companyName": "Acme B.V.",
+                        }
+                    ],
+                    "article": [
+                        {"description": "Widget", "quantity": "1", "price": "100.00"},
+                    ],
+                },
+            },
+        )
+
+        # Route is optional and NL/B2B only - selects ABN-AMRO Achteraf Betalen
+        # instead of the default In3 acquirer.
+        builder.add_parameter("route", "abn_b2b")
+
+        response = builder.pay()
+
+        print(f"   status.code={response.status.code.code}  key={response.key}")
+    except Exception as e:
+        print(f"   ❌ {e}")
+
+
+def main() -> None:
+    print("BUCKAROO SDK — ABN-AMRO ACHTERAF BETALEN DEMO")
+    print("=" * 60)
+    print("Env vars read:")
+    print("  BUCKAROO_STORE_KEY, BUCKAROO_SECRET_KEY, BUCKAROO_MODE")
+
+    demo_abn_amro_achteraf_betalen()
+
+    print("\n" + "=" * 60)
+    print("done.")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests/unit/builders/payments/test_in3_builder.py b/tests/unit/builders/payments/test_in3_builder.py
index fef7206..ecaa087 100644
--- a/tests/unit/builders/payments/test_in3_builder.py
+++ b/tests/unit/builders/payments/test_in3_builder.py
@@ -43,9 +43,21 @@ def test_get_allowed_service_parameters_pay_snapshot(client):
             "required": True,
             "description": "IN3 articles",
         },
+        "route": {
+            "type": str,
+            "required": False,
+            "description": ("In3 acquirer route, e.g. 'abn_b2b' for ABN-AMRO Achteraf Betalen"),
+        },
     }
 
 
+def test_get_allowed_service_parameters_pay_allows_optional_route(client):
+    allowed = In3Builder(client).get_allowed_service_parameters("Pay")
+
+    assert "route" in allowed
+    assert allowed["route"]["required"] is False
+
+
 def test_get_allowed_service_parameters_pay_is_case_insensitive(client):
     builder = In3Builder(client)
 
@@ -59,6 +71,37 @@ def test_get_allowed_service_parameters_non_pay_returns_empty(client, action):
     assert In3Builder(client).get_allowed_service_parameters(action) == {}
 
 
+def test_build_pay_with_route_keeps_route_parameter(client):
+    request = (
+        populate_required_fields(In3Builder(client), amount=99.95)
+        .add_parameter("billingCustomer", [{"Name": "John"}])
+        .add_parameter("shippingCustomer", [{"Name": "John"}])
+        .add_parameter("article", [{"Description": "Widget", "Quantity": 1}])
+        .add_parameter("route", "abn_b2b")
+        .build("Pay")
+    )
+
+    service = request.services.services[0]
+    route_params = [p for p in service.parameters if p.name == "Route"]
+
+    assert len(route_params) == 1
+    assert route_params[0].value == "abn_b2b"
+
+
+def test_build_pay_without_route_is_unchanged(client):
+    request = (
+        populate_required_fields(In3Builder(client), amount=99.95)
+        .add_parameter("billingCustomer", [{"Name": "John"}])
+        .add_parameter("shippingCustomer", [{"Name": "John"}])
+        .add_parameter("article", [{"Description": "Widget", "Quantity": 1}])
+        .build("Pay")
+    )
+
+    service = request.services.services[0]
+
+    assert all(p.name != "Route" for p in service.parameters)
+
+
 def test_pay_posts_transaction_and_parses_response(client, mock_strategy):
     mock_strategy.queue(
         BuckarooMockRequest.json(