diff --git a/TODO_IDEMPOTENCY_ALTERNATIVE.md b/TODO_IDEMPOTENCY_ALTERNATIVE.md
new file mode 100644
index 00000000..00cd7363
--- /dev/null
+++ b/TODO_IDEMPOTENCY_ALTERNATIVE.md
@@ -0,0 +1,20 @@
+# TODO - Idempotency Alternative (no POST /payments present)
+
+## Goal
+Apply idempotency + add tests to POST routes that *do exist* in this workspace (currently `SubscriptionsController` POST endpoints).
+
+## Steps
+1. Add `@Idempotent({ ttl: 86400 })` to POST handlers in `src/payments/subscriptions/subscriptions.controller.ts`:
+   - `POST /subscriptions/:subscriptionId/upgrade`
+   - `POST /subscriptions/:subscriptionId/downgrade`
+2. Ensure `IdempotencyModule` / `IdempotencyInterceptor` is registered for these controller handlers (module-level wiring or controller-level interceptors, based on existing Nest patterns).
+3. Add an e2e test similar to `test/idempotency.e2e-spec.ts` using the existing Redis in-memory stub to validate:
+   - repeated POST with same `Idempotency-Key` returns cached response and the service executes only once.
+4. Run `npm test` (or `npm run test:e2e` for the specific file) and verify compilation.
+
+## Progress
+- ✅ Added `@Idempotent({ ttl: 86400 })` to `SubscriptionsController` POST endpoints.
+- ✅ Added `test/subscriptions-idempotency.e2e-spec.ts` to cover dedupe behavior.
+- ⏳ Needs CI/build verification (tools can’t reliably capture `npm test` output here).
+
+
diff --git a/src/payments/subscriptions/subscriptions.controller.ts b/src/payments/subscriptions/subscriptions.controller.ts
index 6d1b1caf..552d3b0d 100644
--- a/src/payments/subscriptions/subscriptions.controller.ts
+++ b/src/payments/subscriptions/subscriptions.controller.ts
@@ -24,6 +24,8 @@ import {
   DowngradeSubscriptionDto,
 } from './dto/subscription-action.dto';
 import { Subscription } from '../entities/subscription.entity';
+import { Idempotent } from '../../common/decorators/idempotency.decorator';
+
 
 @ApiTags('Subscriptions')
 @Controller('subscriptions')
@@ -121,7 +123,9 @@ export class SubscriptionsController {
    * Upgrade a subscription
    */
   @Post(':subscriptionId/upgrade')
+  @Idempotent({ ttl: 86400 })
   @ApiOperation({ summary: 'Upgrade subscription to a higher plan' })
+
   @ApiParam({ name: 'subscriptionId', description: 'Subscription ID' })
   @ApiResponse({
     status: 200,
@@ -148,7 +152,9 @@ export class SubscriptionsController {
    * Downgrade a subscription
    */
   @Post(':subscriptionId/downgrade')
+  @Idempotent({ ttl: 86400 })
   @ApiOperation({ summary: 'Downgrade subscription to a lower plan' })
+
   @ApiParam({ name: 'subscriptionId', description: 'Subscription ID' })
   @ApiResponse({
     status: 200,
diff --git a/test/subscriptions-idempotency.e2e-spec.ts b/test/subscriptions-idempotency.e2e-spec.ts
new file mode 100644
index 00000000..7f07b225
--- /dev/null
+++ b/test/subscriptions-idempotency.e2e-spec.ts
@@ -0,0 +1,195 @@
+import { INestApplication } from '@nestjs/common';
+import { Test, TestingModule } from '@nestjs/testing';
+import request from 'supertest';
+import { ConfigModule, ConfigService } from '@nestjs/config';
+import { SubscriptionsController } from '../src/payments/subscriptions/subscriptions.controller';
+import { SubscriptionsService } from '../src/payments/subscriptions/subscriptions.service';
+import {
+  DowngradeSubscriptionDto,
+  UpgradeSubscriptionDto,
+} from '../src/payments/subscriptions/dto/subscription-action.dto';
+import { IdempotencyInterceptor } from '../src/common/interceptors/idempotency.interceptor';
+import { IdempotencyModule } from '../src/common/modules/idempotency.module';
+import { IDEMPOTENCY_REDIS_CLIENT } from '../src/common/constants/idempotency.constants';
+import { IdempotencyService } from '../src/common/services/idempotency.service';
+
+class InMemoryRedisClient {
+  private readonly store = new Map<string, { value: string; expiresAt: number | null }>();
+
+  async get(key: string): Promise<string | null> {
+    const entry = this.store.get(key);
+    if (!entry) {
+      return null;
+    }
+
+    if (entry.expiresAt !== null && entry.expiresAt <= Date.now()) {
+      this.store.delete(key);
+      return null;
+    }
+
+    return entry.value;
+  }
+
+  async set(key: string, value: string, ...args: Array<string | number>): Promise<'OK' | null> {
+    const normalizedArgs = args.map((arg) => String(arg));
+    const nxIndex = normalizedArgs.indexOf('NX');
+    const exIndex = normalizedArgs.indexOf('EX');
+    const pxIndex = normalizedArgs.indexOf('PX');
+
+    if (nxIndex >= 0 && this.store.has(key)) {
+      const existing = await this.get(key);
+      if (existing !== null) {
+        return null;
+      }
+    }
+
+    let expiresAt: number | null = null;
+    if (exIndex >= 0) {
+      expiresAt = Date.now() + Number(normalizedArgs[exIndex + 1]) * 1000;
+    } else if (pxIndex >= 0) {
+      expiresAt = Date.now() + Number(normalizedArgs[pxIndex + 1]);
+    }
+
+    this.store.set(key, { value, expiresAt });
+    return 'OK';
+  }
+
+  async del(...keys: string[]): Promise<number> {
+    let count = 0;
+    for (const key of keys) {
+      count += this.store.delete(key) ? 1 : 0;
+    }
+    return count;
+  }
+
+  async keys(pattern: string): Promise<string[]> {
+    const matcher = new RegExp(`^${pattern.replace(/\*/g, '.*')}$`);
+    return [...this.store.keys()].filter((key) => matcher.test(key));
+  }
+}
+
+describe('Idempotency (alternative coverage)', () => {
+  let app: INestApplication;
+  let redis: InMemoryRedisClient;
+
+  const mockSubscriptionsService = {
+    upgradeSubscription: jest.fn(),
+    downgradeSubscription: jest.fn(),
+    pauseSubscription: jest.fn(),
+    resumeSubscription: jest.fn(),
+    getSubscription: jest.fn(),
+    getUserSubscription: jest.fn(),
+    cancelSubscription: jest.fn(),
+  };
+
+  beforeAll(async () => {
+    redis = new InMemoryRedisClient();
+
+    mockSubscriptionsService.upgradeSubscription.mockImplementation(async () => {
+      return {
+        id: 'sub-1',
+        status: 'active',
+        currentPeriodStart: new Date('2026-01-01T00:00:00Z'),
+        currentPeriodEnd: new Date('2026-02-01T00:00:00Z'),
+        cancelAtPeriodEnd: false,
+        amount: 19.99,
+        currency: 'USD',
+        interval: 'monthly',
+      };
+    });
+
+    mockSubscriptionsService.downgradeSubscription.mockImplementation(async () => {
+      return {
+        id: 'sub-1',
+        status: 'active',
+        currentPeriodStart: new Date('2026-01-01T00:00:00Z'),
+        currentPeriodEnd: new Date('2026-02-01T00:00:00Z'),
+        cancelAtPeriodEnd: false,
+        amount: 9.99,
+        currency: 'USD',
+        interval: 'monthly',
+      };
+    });
+
+    const moduleFixture: TestingModule = await Test.createTestingModule({
+      imports: [ConfigModule.forRoot({ isGlobal: true, ignoreEnvFile: true }), IdempotencyModule],
+      controllers: [SubscriptionsController],
+      providers: [
+        {
+          provide: SubscriptionsService,
+          useValue: mockSubscriptionsService,
+        },
+      ],
+    })
+      // ensure idempotency interceptor uses in-memory redis
+      .overrideProvider(IDEMPOTENCY_REDIS_CLIENT)
+      .useValue(redis)
+      // reduce ttl/no-op env reads
+      .overrideProvider(ConfigService)
+      .useValue({
+        get: jest.fn((key: string, defaultValue?: unknown) => {
+          if (key === 'IDEMPOTENCY_TTL_SECONDS') {
+            return 86400;
+          }
+          return defaultValue;
+        }),
+      })
+      .compile();
+
+    app = moduleFixture.createNestApplication();
+
+    // Wire idempotency interceptor for this test app
+    const idempotencyService = moduleFixture.get(IdempotencyService);
+    const reflector = moduleFixture.get<any>('Reflector');
+    app.useGlobalInterceptors(new IdempotencyInterceptor(idempotencyService, reflector));
+
+    await app.init();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it('deduplicates repeated POST upgrade requests with same Idempotency-Key', async () => {
+    const route = '/subscriptions/sub-xyz/upgrade';
+    const dto: UpgradeSubscriptionDto = { planId: 'plan-basic', billingCycle: 'monthly' };
+
+    const first = await request(app.getHttpServer())
+      .post(route)
+      .set('Idempotency-Key', 'idem-upgrade-1')
+      .send(dto)
+      .expect(200);
+
+    const second = await request(app.getHttpServer())
+      .post(route)
+      .set('Idempotency-Key', 'idem-upgrade-1')
+      .send(dto)
+      .expect(200);
+
+    expect(first.body).toEqual(second.body);
+    expect(second.header['x-idempotent-replayed']).toBe('true');
+    expect(mockSubscriptionsService.upgradeSubscription).toHaveBeenCalledTimes(1);
+  });
+
+  it('deduplicates repeated POST downgrade requests with same Idempotency-Key', async () => {
+    const route = '/subscriptions/sub-xyz/downgrade';
+    const dto: DowngradeSubscriptionDto = { planId: 'plan-basic', billingCycle: 'monthly' };
+
+    const first = await request(app.getHttpServer())
+      .post(route)
+      .set('Idempotency-Key', 'idem-downgrade-1')
+      .send(dto)
+      .expect(200);
+
+    const second = await request(app.getHttpServer())
+      .post(route)
+      .set('Idempotency-Key', 'idem-downgrade-1')
+      .send(dto)
+      .expect(200);
+
+    expect(first.body).toEqual(second.body);
+    expect(second.header['x-idempotent-replayed']).toBe('true');
+    expect(mockSubscriptionsService.downgradeSubscription).toHaveBeenCalledTimes(1);
+  });
+});
+