diff --git a/app/main.py b/app/main.py
index 2bca5dc..f94f105 100644
--- a/app/main.py
+++ b/app/main.py
@@ -1,10 +1,11 @@
 import asyncio
-from fastapi import FastAPI, Request, BackgroundTasks
+from fastapi import FastAPI, Request, BackgroundTasks, Body
 from fastapi.responses import JSONResponse
 from app.logging import get_logger
 from app.admin import router as admin_router
 from app.db import SessionLocal, WebhookEndpoint, RequestLog, DeliveryLog, init_db
 from app.services.engine import engine
+from app.models import IncomingPayload
 from contextlib import asynccontextmanager
 
 logger = get_logger("app")
@@ -64,7 +65,7 @@ async def health():
     return {"status": "ok"}
 
 @app.post("/webhook/{namespace}")
-async def webhook(namespace: str, request: Request, background_tasks: BackgroundTasks):
+async def webhook(namespace: str, payload: IncomingPayload = Body(...), background_tasks: BackgroundTasks = BackgroundTasks()):
     db = SessionLocal()
     endpoint = db.query(WebhookEndpoint).filter(WebhookEndpoint.namespace == namespace).first()
     
@@ -82,16 +83,17 @@ async def webhook(namespace: str, request: Request, background_tasks: Background
     endpoint_id = endpoint.id
     db.close()
 
+    # payload is validated by Pydantic; convert to plain dict for engine
     try:
-        body = await request.json()
+        body_dict = payload.model_dump()
     except Exception:
-        return JSONResponse({"error": "Invalid JSON"}, status_code=400)
+        return JSONResponse({"error": "Invalid payload"}, status_code=400)
 
     # Use new engine
-    routed, notified = await engine.process(endpoint_id, body)
+    routed, notified = await engine.process(endpoint_id, body_dict)
     
     # Async save logs
-    background_tasks.add_task(save_logs, namespace, body, routed, notified)
+    background_tasks.add_task(save_logs, namespace, body_dict, routed, notified)
 
     result = {
         "namespace": namespace,
diff --git a/app/services/engine.py b/app/services/engine.py
index 32d7669..41770b3 100644
--- a/app/services/engine.py
+++ b/app/services/engine.py
@@ -3,6 +3,7 @@ import asyncio
 import re
 from app.db import SessionLocal, ProcessingRule, RuleAction, Target, NotificationChannel, MessageTemplate
 from app.logging import get_logger
+from app.templates import safe_render
 
 logger = get_logger("engine")
 
@@ -100,7 +101,8 @@ class RuleEngine:
                                             render_context = self._flatten_payload(payload)
                                             render_context.update(current_context["vars"])
                                             
-                                            msg = template_content.format(**render_context)
+                                            # Use safe Jinja2 rendering (supports legacy {var} by conversion)
+                                            msg = safe_render(template_content, render_context)
                                             
                                             c_dict = {"channel": action.channel.channel_type, "url": action.channel.webhook_url}
                                             tasks.append(self._exec_notify(c_dict, msg))
diff --git a/tests/test_preview_endpoint.py b/tests/test_preview_endpoint.py
new file mode 100644
index 0000000..c9501d5
--- /dev/null
+++ b/tests/test_preview_endpoint.py
@@ -0,0 +1,23 @@
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def test_preview_endpoint_success():
+    client = TestClient(app)
+    payload = {
+        "template_content": "ok {trans_amt}",
+        "sample_payload": {"trans_amt": 123}
+    }
+    resp = client.post("/admin/templates/preview", json=payload)
+    assert resp.status_code == 200
+    assert resp.json().get("rendered") == "ok 123"
+
+
+def test_preview_endpoint_strict_failure():
+    client = TestClient(app)
+    # Template refers to undefined variable -> StrictUndefined should cause error -> 400
+    payload = {"template_content": "{{ undefined_var }}", "sample_payload": {}}
+    resp = client.post("/admin/templates/preview", json=payload)
+    assert resp.status_code == 400
+