fix: Amplitude list creation response shape (#8402)

Co-authored-by: flagsmith-engineering[bot] <flagsmith-engineering[bot]@users.noreply.github.com>

Author: gagantrivedi

api/cohorts/sync_views.py

@@ -22,7 +22,13 @@
 )
 
 _LIST_RESPONSE = inline_serializer(
-    "AmplitudeListResponse", {"listId": serializers.UUIDField()}
+    "AmplitudeListResponse",
+    {
+        "list_id": serializers.UUIDField(),
+        "response": inline_serializer(
+            "AmplitudeListResponseEnvelope", {"list_id": serializers.UUIDField()}
+        ),
+    },
 )
 
 _MIXPANEL_RESPONSE = inline_serializer(
@@ -73,10 +79,13 @@ def create(self, request: Request) -> Response:
             name=serializer.validated_data["name"],
             source_type=CohortSourceType.AMPLITUDE,
         )
-        # Amplitude's production sync worker reads the list ID from its
-        # documented default key, camelCase "listId", ignoring the response
-        # path configured in the Integration Portal.
-        return Response({"listId": str(cohort.uuid)})
+        # Two different Amplitude systems read this response, and they look
+        # for the list ID in different places: the real cohort sync reads
+        # body["response"]["list_id"], the portal's Testing tab reads
+        # body["list_id"]. Send both so neither breaks. Verified on
+        # staging, 2026-08-31.
+        list_id = str(cohort.uuid)
+        return Response({"list_id": list_id, "response": {"list_id": list_id}})
 
     @action(detail=True, methods=["POST"])
     def add(self, request: Request, pk: str) -> Response:

api/tests/unit/cohorts/test_sync_views.py

@@ -50,7 +50,10 @@ def test_amplitude_create_list__valid_key__creates_amplitude_cohort(
 
     # Then
     assert response.status_code == status.HTTP_200_OK
-    cohort = Cohort.objects.get(uuid=response.json()["listId"])
+    cohort = Cohort.objects.get(uuid=response.json()["list_id"])
+    # Amplitude's production worker reads the nested copy, its Testing tab
+    # the flat one.
+    assert response.json()["response"]["list_id"] == response.json()["list_id"]
     assert cohort.environment == key.environment
     assert cohort.source_type == CohortSourceType.AMPLITUDE
     assert cohort.segment.name == "[Amplitude] Beta users: 1234"
@@ -74,7 +77,7 @@ def test_amplitude_create_list__postgres_environment__creates_cohort(
 
     # Then
     assert response.status_code == status.HTTP_200_OK
-    cohort = Cohort.objects.get(uuid=response.json()["listId"])
+    cohort = Cohort.objects.get(uuid=response.json()["list_id"])
     assert cohort.environment == environment
 
 
@@ -350,7 +353,7 @@ def test_amplitude_create_list__valid_key__audits_and_queues_environment_update(
     # Then - the audit record carries no user, names the source, and is the
     # hook that rebuilds the environment document.
     assert response.status_code == status.HTTP_200_OK
-    cohort = Cohort.objects.get(uuid=response.json()["listId"])
+    cohort = Cohort.objects.get(uuid=response.json()["list_id"])
     audit_log = AuditLog.objects.get(related_object_id=cohort.segment_id)
     assert audit_log.author is None
     assert audit_log.master_api_key is None
@@ -377,7 +380,7 @@ def test_amplitude_create_list__valid_key__history_records_no_user(
     # Then - a machine caller leaves no user on historical records; stamping
     # one would fail, since the sync key is not a Flagsmith user.
     assert response.status_code == status.HTTP_200_OK
-    cohort = Cohort.objects.get(uuid=response.json()["listId"])
+    cohort = Cohort.objects.get(uuid=response.json()["list_id"])
     history_record = cohort.segment.history.get()
     assert history_record.history_user is None
     assert history_record.master_api_key is None

docs/docs/deployment-self-hosting/observability/_events-catalogue.md

@@ -166,7 +166,7 @@ Attributes:
 ### `cohorts.sync_webhook.rejected`
 
 Logged at `warning` from:
- - `api/cohorts/sync_views.py:217`
+ - `api/cohorts/sync_views.py:226`
 
 Attributes:
  - `action`

openapi.yaml

@@ -18943,11 +18943,22 @@ components:
     AmplitudeListResponse:
       type: object
       properties:
-        listId:
+        list_id:
           type: string
           format: uuid
+        response:
+          $ref: '#/components/schemas/AmplitudeListResponseEnvelope'
       required:
-        - listId
+        - list_id
+        - response
+    AmplitudeListResponseEnvelope:
+      type: object
+      properties:
+        list_id:
+          type: string
+          format: uuid
+      required:
+        - list_id
     AuditLogList:
       type: object
       properties: