diff --git a/dashboard/src/store/eventStore.test.tsx b/dashboard/src/store/eventStore.test.tsx
index a2128c4..03ce4d6 100644
--- a/dashboard/src/store/eventStore.test.tsx
+++ b/dashboard/src/store/eventStore.test.tsx
@@ -70,6 +70,7 @@ describe('pagination + filter interaction', () => {
     const events = generateMockEvents(200);
     useEventStore.setState({
       events,
+      filters: { search: '', contractAddress: 'all', eventType: 'all' },
       filters: { search: '', contractAddress: 'all', eventType: 'all', status: 'all', dateFrom: '', dateTo: '' },
       isLoading: false,
       error: null,
@@ -93,6 +94,7 @@ describe('pagination + filter interaction', () => {
   it('filter change resets scroll position to top', async () => {
     useEventStore.setState({
       events: generateMockEvents(100),
+      filters: { search: '', contractAddress: 'all', eventType: 'all' },
       filters: { search: '', contractAddress: 'all', eventType: 'all', status: 'all', dateFrom: '', dateTo: '' },
       isLoading: false,
       error: null,
diff --git a/listener/src/services/notification-scheduler.ts b/listener/src/services/notification-scheduler.ts
index 9109ba0..b7443a6 100644
--- a/listener/src/services/notification-scheduler.ts
+++ b/listener/src/services/notification-scheduler.ts
@@ -254,6 +254,30 @@ export class NotificationScheduler {
         return;
       }
 
+      // Verify payload integrity before executing
+      const secret = process.env.PAYLOAD_INTEGRITY_SECRET;
+      if (secret) {
+        if (!notification.payloadHash) {
+          logger.warn('Payload integrity check skipped — no hash stored', {
+            requestId,
+            id: notification.id,
+          });
+        } else if (!verifyPayloadIntegrity(notification.payload, notification.payloadHash, secret)) {
+          logger.error('Payload integrity verification failed — rejecting notification', {
+            requestId,
+            id: notification.id,
+            type: notification.notificationType,
+          });
+          await this.repository.markAsFailedOrRetry(
+            notification.id!,
+            new Error('Payload integrity check failed: hash mismatch'),
+            notification.maxRetries, // exhaust retries — don't retry a tampered payload
+            notification.maxRetries
+          );
+          return;
+        }
+      }
+
       // Execute notification based on type
       const success = await this.executeNotification(notification, requestId);
 
diff --git a/listener/src/services/scheduled-notification-repository.ts b/listener/src/services/scheduled-notification-repository.ts
index 5dcbb08..e76d03b 100644
--- a/listener/src/services/scheduled-notification-repository.ts
+++ b/listener/src/services/scheduled-notification-repository.ts
@@ -7,6 +7,7 @@ import {
   NotificationStatus,
   NotificationExecutionLog,
 } from '../types/scheduled-notification';
+import { hashPayload } from '../utils/payload-integrity';
 
 /**
  * Repository for scheduled notifications database operations
@@ -19,15 +20,20 @@ export class ScheduledNotificationRepository {
    * Create a new scheduled notification
    */
   async create(input: CreateScheduledNotificationInput, requestId?: string): Promise<number> {
+    const payloadJson = JSON.stringify(input.payload);
+    const secret = process.env.PAYLOAD_INTEGRITY_SECRET;
+    const payloadHash = secret ? hashPayload(payloadJson, secret) : null;
+
     const sql = `
       INSERT INTO scheduled_notifications (
-        payload, notification_type, target_recipient, execute_at,
+        payload, payload_hash, notification_type, target_recipient, execute_at,
         max_retries, event_id, contract_address, priority, metadata
-      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
+      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
     `;
 
     const params = [
-      JSON.stringify(input.payload),
+      payloadJson,
+      payloadHash,
       input.notificationType,
       input.targetRecipient,
       input.executeAt.toISOString(),
@@ -490,6 +496,7 @@ export class ScheduledNotificationRepository {
     return {
       id: row.id,
       payload: row.payload,
+      payloadHash: row.payload_hash,
       notificationType: row.notification_type as any,
       targetRecipient: row.target_recipient,
       executeAt: new Date(row.execute_at),
diff --git a/listener/src/tests/payload-integrity.test.ts b/listener/src/tests/payload-integrity.test.ts
new file mode 100644
index 0000000..755b6b8
--- /dev/null
+++ b/listener/src/tests/payload-integrity.test.ts
@@ -0,0 +1,154 @@
+import { hashPayload, verifyPayloadIntegrity } from '../utils/payload-integrity';
+import { Database } from '../database/database';
+import { ScheduledNotificationRepository } from '../services/scheduled-notification-repository';
+import { NotificationAPI } from '../services/notification-api';
+import { NotificationType } from '../types/scheduled-notification';
+import * as fs from 'fs';
+import * as path from 'path';
+
+const SECRET = 'test-secret-key';
+const TEST_DB = './data/test-integrity.db';
+
+// ─── Unit tests ──────────────────────────────────────────────────────────────
+
+describe('hashPayload', () => {
+  it('produces a hex string', () => {
+    const hash = hashPayload('{"foo":"bar"}', SECRET);
+    expect(hash).toMatch(/^[a-f0-9]{64}$/);
+  });
+
+  it('is deterministic', () => {
+    const payload = '{"event":"test"}';
+    expect(hashPayload(payload, SECRET)).toBe(hashPayload(payload, SECRET));
+  });
+
+  it('differs when payload changes', () => {
+    expect(hashPayload('{"a":1}', SECRET)).not.toBe(hashPayload('{"a":2}', SECRET));
+  });
+
+  it('differs when secret changes', () => {
+    const payload = '{"a":1}';
+    expect(hashPayload(payload, 'secret-a')).not.toBe(hashPayload(payload, 'secret-b'));
+  });
+});
+
+describe('verifyPayloadIntegrity', () => {
+  it('returns true for a valid payload/hash pair', () => {
+    const payload = '{"message":"hello"}';
+    const hash = hashPayload(payload, SECRET);
+    expect(verifyPayloadIntegrity(payload, hash, SECRET)).toBe(true);
+  });
+
+  it('returns false when payload is tampered', () => {
+    const original = '{"amount":100}';
+    const hash = hashPayload(original, SECRET);
+    expect(verifyPayloadIntegrity('{"amount":999}', hash, SECRET)).toBe(false);
+  });
+
+  it('returns false when hash is wrong', () => {
+    const payload = '{"ok":true}';
+    expect(verifyPayloadIntegrity(payload, 'deadbeef', SECRET)).toBe(false);
+  });
+
+  it('returns false for empty payload', () => {
+    expect(verifyPayloadIntegrity('', hashPayload('', SECRET), SECRET)).toBe(false);
+  });
+
+  it('returns false for empty hash', () => {
+    expect(verifyPayloadIntegrity('{"x":1}', '', SECRET)).toBe(false);
+  });
+});
+
+// ─── Integration tests ───────────────────────────────────────────────────────
+
+describe('payload integrity — repository and scheduler integration', () => {
+  let db: Database;
+  let repository: ScheduledNotificationRepository;
+  let api: NotificationAPI;
+
+  beforeAll(async () => {
+    process.env.PAYLOAD_INTEGRITY_SECRET = SECRET;
+
+    const dir = path.dirname(TEST_DB);
+    if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });
+    if (fs.existsSync(TEST_DB)) fs.unlinkSync(TEST_DB);
+
+    db = new Database(TEST_DB);
+    await db.initialize();
+    repository = new ScheduledNotificationRepository(db);
+    api = new NotificationAPI(repository);
+  });
+
+  afterAll(async () => {
+    delete process.env.PAYLOAD_INTEGRITY_SECRET;
+    await db.close();
+    if (fs.existsSync(TEST_DB)) fs.unlinkSync(TEST_DB);
+  });
+
+  beforeEach(async () => {
+    await db.run('DELETE FROM notification_execution_log');
+    await db.run('DELETE FROM scheduled_notifications');
+  });
+
+  it('stores a payload_hash when secret is set', async () => {
+    const id = await api.scheduleNotification({
+      payload: { message: 'hello' },
+      notificationType: NotificationType.DISCORD,
+      targetRecipient: 'https://discord.com/webhook/test',
+      executeAt: new Date(Date.now() + 60000),
+    });
+
+    const notification = await repository.getById(id);
+    expect(notification!.payloadHash).toBeTruthy();
+    expect(notification!.payloadHash).toMatch(/^[a-f0-9]{64}$/);
+  });
+
+  it('stored hash matches the payload', async () => {
+    const payload = { message: 'integrity check' };
+    const id = await api.scheduleNotification({
+      payload,
+      notificationType: NotificationType.DISCORD,
+      targetRecipient: 'https://discord.com/webhook/test',
+      executeAt: new Date(Date.now() + 60000),
+    });
+
+    const notification = await repository.getById(id);
+    const expected = hashPayload(JSON.stringify(payload), SECRET);
+    expect(notification!.payloadHash).toBe(expected);
+  });
+
+  it('detects a tampered payload', async () => {
+    const id = await api.scheduleNotification({
+      payload: { amount: 100 },
+      notificationType: NotificationType.DISCORD,
+      targetRecipient: 'https://discord.com/webhook/test',
+      executeAt: new Date(Date.now() + 60000),
+    });
+
+    // Tamper directly in the DB
+    await db.run('UPDATE scheduled_notifications SET payload = ? WHERE id = ?', [
+      JSON.stringify({ amount: 999 }),
+      id,
+    ]);
+
+    const notification = await repository.getById(id);
+    expect(
+      verifyPayloadIntegrity(notification!.payload, notification!.payloadHash!, SECRET)
+    ).toBe(false);
+  });
+
+  it('verifies an untampered payload successfully', async () => {
+    const payload = { event: 'TaskCreated', ledger: 42 };
+    const id = await api.scheduleNotification({
+      payload,
+      notificationType: NotificationType.DISCORD,
+      targetRecipient: 'https://discord.com/webhook/test',
+      executeAt: new Date(Date.now() + 60000),
+    });
+
+    const notification = await repository.getById(id);
+    expect(
+      verifyPayloadIntegrity(notification!.payload, notification!.payloadHash!, SECRET)
+    ).toBe(true);
+  });
+});
diff --git a/listener/src/types/scheduled-notification.ts b/listener/src/types/scheduled-notification.ts
index a521865..cfdb55f 100644
--- a/listener/src/types/scheduled-notification.ts
+++ b/listener/src/types/scheduled-notification.ts
@@ -20,6 +20,7 @@ export enum NotificationType {
 export interface ScheduledNotification {
   id?: number;
   payload: string; // JSON string
+  payloadHash?: string | null;
   notificationType: NotificationType;
   targetRecipient: string;
   executeAt: Date;
@@ -57,6 +58,7 @@ export interface CreateScheduledNotificationInput {
 export interface ScheduledNotificationRow {
   id: number;
   payload: string;
+  payload_hash: string | null;
   notification_type: string;
   target_recipient: string;
   execute_at: string;
diff --git a/listener/src/utils/payload-integrity.ts b/listener/src/utils/payload-integrity.ts
new file mode 100644
index 0000000..6d3ad60
--- /dev/null
+++ b/listener/src/utils/payload-integrity.ts
@@ -0,0 +1,27 @@
+import crypto from 'crypto';
+
+/**
+ * Computes an HMAC-SHA256 hash of a payload string.
+ * The secret should come from the PAYLOAD_INTEGRITY_SECRET env var.
+ */
+export function hashPayload(payload: string, secret: string): string {
+  return crypto.createHmac('sha256', secret).update(payload, 'utf8').digest('hex');
+}
+
+/**
+ * Verifies that a payload matches its stored hash using a timing-safe comparison.
+ * Returns false if either argument is missing or the hash doesn't match.
+ */
+export function verifyPayloadIntegrity(
+  payload: string,
+  storedHash: string,
+  secret: string
+): boolean {
+  if (!payload || !storedHash) return false;
+
+  const expected = hashPayload(payload, secret);
+
+  if (expected.length !== storedHash.length) return false;
+
+  return crypto.timingSafeEqual(Buffer.from(expected, 'utf8'), Buffer.from(storedHash, 'utf8'));
+}