diff --git a/examples/customer-support/backend/app/airline_state.py b/examples/customer-support/backend/app/airline_state.py
index eaa83287..9f9d9656 100644
--- a/examples/customer-support/backend/app/airline_state.py
+++ b/examples/customer-support/backend/app/airline_state.py
@@ -120,10 +120,12 @@ def change_seat(self, thread_id: str, flight_number: str, seat: str) -> str:
         )
         return f"Seat updated to {segment.seat} on flight {segment.flight_number}."
 
-    def cancel_trip(self, thread_id: str) -> str:
+    def cancel_trip(self, thread_id: str, flight_number: str) -> str:
         profile = self.get_profile(thread_id)
-        for segment in profile.segments:
-            segment.cancel()
+        segment = self._find_segment(profile, flight_number)
+        if segment is None:
+            raise ValueError(f"Flight {flight_number} is not on the customer's itinerary.")
+        segment.cancel()
         profile.log("Trip cancelled at customer request.", kind="warning")
         return "The reservation has been cancelled. Refund processing will begin immediately."
 
diff --git a/examples/customer-support/backend/app/support_agent.py b/examples/customer-support/backend/app/support_agent.py
index b8ac0f4c..47e5b8e2 100644
--- a/examples/customer-support/backend/app/support_agent.py
+++ b/examples/customer-support/backend/app/support_agent.py
@@ -29,7 +29,7 @@
 
 Available tools:
 - change_seat(flight_number: str, seat: str) – move the passenger to a new seat.
-- cancel_trip() – cancel the upcoming reservation and note the refund.
+- cancel_trip(flight_number: str) – cancel the upcoming reservation and note the refund.
 - add_checked_bag() – add one checked bag to the itinerary.
 - meal_preference_list() – show meal options so the traveller can pick their preference.
   Invoke this tool when the user requests to set or change their meal preference or option.
@@ -63,8 +63,11 @@ async def change_seat(
     @function_tool(
         description_override="Cancel the traveller's upcoming trip and note the refund.",
     )
-    async def cancel_trip(ctx: RunContextWrapper[AgentContext]) -> Dict[str, str]:
-        message = state_manager.cancel_trip(_thread_id(ctx))
+    async def cancel_trip(ctx: RunContextWrapper[AgentContext], flight_number: str) -> Dict[str, str]:
+        try:
+            message = state_manager.cancel_trip(_thread_id(ctx), flight_number)
+        except ValueError as exc:  # translate user errors
+            raise ValueError(str(exc)) from exc
         return {"result": message}
 
     @function_tool(