diff --git a/enrollment-management/app/events/stopgap/del_vacancies.py b/enrollment-management/app/events/stopgap/del_vacancies.py
index fb9ac7e..deaa5eb 100644
--- a/enrollment-management/app/events/stopgap/del_vacancies.py
+++ b/enrollment-management/app/events/stopgap/del_vacancies.py
@@ -32,7 +32,7 @@ def lambda_handler(event: EventBridgeEvent, context: LambdaContext) -> bool:
         + KeyPair(
             pk=order_id,
             sk=SortKey(
-                'metadata#tenant',
+                sk='metadata#tenant',
                 path_spec='tenant_id',
                 remove_prefix='metadata#',
             ),
@@ -61,7 +61,7 @@ def lambda_handler(event: EventBridgeEvent, context: LambdaContext) -> bool:
         for pair in result['items']:
             batch.delete_item(
                 Key={
-                    'id': {'S': f'vacancies#{pair["id"]}'},
+                    'id': {'S': ComposeKey(pair['id'], prefix='vacancies')},
                     'sk': {'S': pair['sk']},
                 }
             )
diff --git a/enrollment-management/template.yaml b/enrollment-management/template.yaml
index 0e338c4..610019b 100644
--- a/enrollment-management/template.yaml
+++ b/enrollment-management/template.yaml
@@ -20,7 +20,7 @@ Globals:
     Architectures:
       - x86_64
     Layers:
-      - !Sub arn:aws:lambda:sa-east-1:336641857101:layer:layercake:72
+      - !Sub arn:aws:lambda:sa-east-1:336641857101:layer:layercake:75
     Environment:
       Variables:
         TZ: America/Sao_Paulo
diff --git a/enrollment-management/uv.lock b/enrollment-management/uv.lock
index 7526fe8..10b9ce1 100644
--- a/enrollment-management/uv.lock
+++ b/enrollment-management/uv.lock
@@ -522,7 +522,7 @@ wheels = [
 
 [[package]]
 name = "layercake"
-version = "0.6.2"
+version = "0.6.5"
 source = { directory = "../layercake" }
 dependencies = [
     { name = "arnparse" },
diff --git a/http-api/app/app.py b/http-api/app/app.py
index 91e18bc..0fd3199 100644
--- a/http-api/app/app.py
+++ b/http-api/app/app.py
@@ -1,20 +1,36 @@
+import json
 import os
+from datetime import date
+from functools import partial
 from typing import Any
 
 from aws_lambda_powertools import Logger, Tracer
 from aws_lambda_powertools.event_handler.api_gateway import (
     APIGatewayHttpResolver,
     CORSConfig,
-    Response,
-    content_types,
 )
 from aws_lambda_powertools.event_handler.exceptions import ServiceError
 from aws_lambda_powertools.logging import correlation_paths
 from aws_lambda_powertools.utilities.typing import LambdaContext
 
+from api_gateway import JSONResponse
 from middlewares import AuthenticationMiddleware
 from routes import courses, enrollments, lookup, orders, orgs, settings, users, webhooks
 
+
+class JSONEncoder(json.JSONEncoder):
+    def default(self, o):
+        if isinstance(o, date):
+            return o.isoformat()
+
+        return super().default(o)
+
+
+def foo(obj):
+    print(obj)
+    return json.dumps(obj, separators=(',', ':'), cls=JSONEncoder)
+
+
 tracer = Tracer()
 logger = Logger(__name__)
 cors = CORSConfig(
@@ -27,6 +43,7 @@ app = APIGatewayHttpResolver(
     enable_validation=True,
     cors=cors,
     debug='AWS_SAM_LOCAL' in os.environ,
+    serializer=partial(json.dumps, separators=(',', ':'), cls=JSONEncoder),
 )
 app.use(middlewares=[AuthenticationMiddleware()])
 app.include_router(courses.router, prefix='/courses')
@@ -47,12 +64,11 @@ app.include_router(lookup.router, prefix='/lookup')
 
 @app.exception_handler(ServiceError)
 def exc_error(exc: ServiceError):
-    return Response(
+    return JSONResponse(
         body={
-            'msg': exc.msg,
-            'err': type(exc).__name__,
+            'type': type(exc).__name__,
+            'message': str(exc),
         },
-        content_type=content_types.APPLICATION_JSON,
         status_code=exc.status_code,
     )
 
diff --git a/http-api/app/routes/enrollments/enroll.py b/http-api/app/routes/enrollments/enroll.py
index 8b0605a..b3b27fa 100644
--- a/http-api/app/routes/enrollments/enroll.py
+++ b/http-api/app/routes/enrollments/enroll.py
@@ -51,18 +51,9 @@ def enroll_(payload: Payload):
     context = {'tenant': router.context['tenant']}
 
     with processor(payload.items, handler, context):
-        processor.process()
+        processed_messages = processor.process()
 
-    print(processor.exceptions)
-
-    return JSONResponse(
-        HTTPStatus.OK,
-        {
-            'successes': processor.successes,
-            'failures': processor.failures,
-            'exceptions': [str(exc) for exc in processor.exceptions],
-        },
-    )
+    return JSONResponse(HTTPStatus.OK, processed_messages)
 
 
 def handler(record: Item, context: dict):
diff --git a/http-api/app/rules/enrollment.py b/http-api/app/rules/enrollment.py
index ed6655e..4a9ca34 100644
--- a/http-api/app/rules/enrollment.py
+++ b/http-api/app/rules/enrollment.py
@@ -63,6 +63,7 @@ def enroll(
     user = enrollment.user
     course = enrollment.course
     tenant_id = tenant['id']
+    lock_hash = md5_hash('%s%s' % (user.id, course.id))
 
     with persistence_layer.transact_writer() as transact:
         transact.put(
@@ -117,19 +118,24 @@ def enroll(
             },
         )
 
+        class DeduplicationConflictError(Exception):
+            def __init__(self, *args):
+                super().__init__('Enrollment already exists')
+
         # Prevents the user from enrolling in the same course again until
         # the deduplication window expires or is removed
+        transact.condition(
+            key=KeyPair('lock', lock_hash),
+            cond_expr='attribute_not_exists(sk)',
+            exc_cls=DeduplicationConflictError,
+        )
+
         if deduplication_window:
-            lock_hash = md5_hash('%s%s' % (user.id, course.id))
             offset_days = deduplication_window['offset_days']
             ttl_expiration = ttl(
                 start_dt=now_ + timedelta(days=course.access_period - offset_days)
             )
 
-            class DeduplicationConflictError(Exception):
-                def __init__(self, *args):
-                    super().__init__('Enrollment already exists')
-
             transact.put(
                 item={
                     'id': 'lock',
@@ -138,8 +144,6 @@ def enroll(
                     'create_date': now_,
                     'ttl': ttl_expiration,
                 },
-                cond_expr='attribute_not_exists(sk)',
-                exc_cls=DeduplicationConflictError,
             )
             transact.put(
                 item={
diff --git a/http-api/template.yaml b/http-api/template.yaml
index 3f0b7cf..2dedba9 100644
--- a/http-api/template.yaml
+++ b/http-api/template.yaml
@@ -23,7 +23,7 @@ Globals:
     Architectures:
       - x86_64
     Layers:
-      - !Sub arn:aws:lambda:sa-east-1:336641857101:layer:layercake:72
+      - !Sub arn:aws:lambda:sa-east-1:336641857101:layer:layercake:75
     Environment:
       Variables:
         TZ: America/Sao_Paulo
diff --git a/http-api/tests/routes/test_enrollments.py b/http-api/tests/routes/test_enrollments.py
index 5db04c7..5f8ee18 100644
--- a/http-api/tests/routes/test_enrollments.py
+++ b/http-api/tests/routes/test_enrollments.py
@@ -26,6 +26,7 @@ def test_enroll(
             headers={'X-Tenant': 'cJtK9SsnJhKPyxESe7g3DG'},
             body={
                 'items': [
+                    # existing enrollment, must fail
                     {
                         'user': {
                             'id': '5OxmMjL-ujoR5IMGegQz',
@@ -37,9 +38,6 @@ def test_enroll(
                             'id': '6d69a34a-cefd-40aa-a89b-dceb694c3e61',
                             'name': 'pytest',
                         },
-                        'deduplication_window': {
-                            'offset_days': 60,
-                        },
                     },
                     {
                         'user': {
@@ -52,6 +50,9 @@ def test_enroll(
                             'id': '6d69a34a-cefd-40aa-a89b-dceb694c3e61',
                             'name': 'pytest',
                         },
+                        'deduplication_window': {
+                            'offset_days': 60,
+                        },
                     },
                 ],
             },
@@ -59,8 +60,13 @@ def test_enroll(
         lambda_context,
     )
 
-    # assert r['statusCode'] == HTTPStatus.OK
-    print(json.loads(r['body']))
+    assert r['statusCode'] == HTTPStatus.OK
+
+    fail, _ = json.loads(r['body'])
+    assert fail['cause'] == {
+        'type': 'DeduplicationConflictError',
+        'message': 'Enrollment already exists',
+    }
 
 
 def test_vacancies(
diff --git a/http-api/uv.lock b/http-api/uv.lock
index 34bb53a..b312853 100644
--- a/http-api/uv.lock
+++ b/http-api/uv.lock
@@ -560,7 +560,7 @@ wheels = [
 
 [[package]]
 name = "layercake"
-version = "0.6.2"
+version = "0.6.5"
 source = { directory = "../layercake" }
 dependencies = [
     { name = "arnparse" },
diff --git a/user-management/app/ses_utils.py b/user-management/app/ses_utils.py
new file mode 100644
index 0000000..04a6580
--- /dev/null
+++ b/user-management/app/ses_utils.py
@@ -0,0 +1,20 @@
+from typing import Any, Iterator
+
+from aws_lambda_powertools.utilities.data_classes.ses_event import SESMailHeader
+
+
+def get_header_value(
+    headers: Iterator[SESMailHeader],
+    header_name: str,
+    *,
+    default: Any = None,
+    raise_on_missing: bool = True,
+) -> str:
+    for header in headers:
+        if header.name.lower() == header_name:
+            return header.value
+
+    if raise_on_missing:
+        raise ValueError(f'{header_name} not found.')
+
+    return default
diff --git a/user-management/tests/seeds.jsonl b/user-management/tests/seeds.jsonl
new file mode 100644
index 0000000..b704442
--- /dev/null
+++ b/user-management/tests/seeds.jsonl
@@ -0,0 +1,4 @@
+{"id": {"S": "cJtK9SsnJhKPyxESe7g3DG"}, "sk": {"S": "0"}, "name": {"S": "EDUSEG"}}
+{"id": {"S": "cJtK9SsnJhKPyxESe7g3DG"}, "sk": {"S": "admins#5OxmMjL-ujoR5IMGegQz"}, "name": {"S": "Sérgio R Siqueira"}, "email": {"S": "sergio@somosbeta.com.br"}}
+{"id": {"S": "cnpj"}, "sk": {"S": "15608435000190"}, "user_id": {"S": "cJtK9SsnJhKPyxESe7g3DG"}}
+{"id": {"S": "email"}, "sk": {"S": "org+15608435000190@users.noreply.saladeaula.digital"}, "user_id": {"S": "cJtK9SsnJhKPyxESe7g3DG"}}
\ No newline at end of file