How to migrate from Stripe to Polar in 2 hours

If you have an indie SaaS selling to Europe, you've probably felt the pull to migrate from Stripe to Polar. The main reason: Polar is a Merchant of Record and takes VAT off your hands.

The technical migration isn't as painful as it sounds. If your Stripe integration is well modularized, it's ~2 hours of work. This guide explains how we'd do it in an existing Next.js app.

Before migrating: what does NOT move

• Active subscriptions: don't migrate automatically. Polar doesn't import from Stripe. Existing customers stay on Stripe until they renew or change plans.
• Payment history: not transferred. Leave it on Stripe as archive.
• Saved payment methods: not either. Polar will ask for the card again.

That's why migration works best with a young SaaS (< 100 subscriptions) or with a gradual switch: new customers on Polar, old ones stay on Stripe until churn.

Step 1: install Polar

bun add @polar-sh/sdk

Keep stripe for now; you'll remove it at the end.

Step 2: environment variables

Keep Stripe's and add Polar's:

POLAR_ACCESS_TOKEN=polar_oat_...
POLAR_WEBHOOK_SECRET=whsec_...
POLAR_SERVER=production

Step 3: create products in Polar Dashboard

Replicate the products you have in Stripe. Watch out for:

• Prices: Polar works in cents like Stripe. But if you have VAT-included prices in Stripe, in Polar you put the net price and Polar adds VAT to the end customer. Decide if your visible pricing changes.
• Recurring intervals: monthly, yearly. Polar supports them.
• One-time products: also supported, like Stripe.

Step 4: abstract the payments logic

If you already have an abstraction layer like PaymentService or lib/payments/, you've got this done. If not, now is the time.

src/lib/payments/types.ts:

export interface PaymentProvider {
  createCheckout(params: CheckoutParams): Promise<{ url: string }>;
  cancelSubscription(subscriptionId: string): Promise<void>;
  verifyWebhook(body: string, signature: string): Promise<WebhookEvent>;
}

Implement StripeProvider and PolarProvider. Switch between them with an env var:

const provider =
  process.env.PAYMENT_PROVIDER === 'polar' ? new PolarProvider() : new StripeProvider();

Step 5: new Polar webhook endpoint

Stripe and Polar sign webhooks differently. Create a new endpoint, don't modify the Stripe one:

src/app/api/webhooks/polar/route.ts:

import { polar } from '@/lib/polar/client';
import { db } from '@/lib/db/client';

export async function POST(req: Request) {
  const body = await req.text();
  const signature = req.headers.get('webhook-signature')!;

  const event = polar.webhooks.verify({
    body,
    signature,
    secret: process.env.POLAR_WEBHOOK_SECRET!,
  });

  // Reuse the logic from your Stripe webhook, adapted to Polar events
  switch (event.type) {
    case 'subscription.created':
      // create in DB
      break;
    case 'subscription.canceled':
      // mark as canceled
      break;
  }

  return new Response('OK');
}

Step 6: cohort strategy

In your DB, add a paymentProvider field to the subscriptions table:

model Subscription {
  id              String   @id
  userId          String
  paymentProvider String   // 'stripe' | 'polar'
  externalId      String   // ID in Stripe or Polar
  status          String
  ...
}

When a user cancels and re-subscribes, their new subscription goes to Polar. Old ones stay on Stripe until natural churn.

Step 7: test in sandbox

Polar has a separate sandbox. Before touching production:

1. Create a sandbox account + products in sandbox
2. Set POLAR_SERVER=sandbox
3. Make a test purchase with card 4242 4242 4242 4242
4. Verify the webhook arrives and DB updates
5. Verify cancellation

When everything works in sandbox → switch to production.

Step 8: shadow deploy

Don't announce the migration on day 1. Deploy Polar to production with:

• "Pay with Polar" button hidden behind a feature flag
• Enable the flag for your test account
• Make a real purchase
• Verify Polar transfers the money to your bank account
• Enable for all new signups

Common errors

1. Webhook deduplication: if you replay the same event, make sure your DB doesn't create duplicate subscriptions. Index by externalId.

2. VAT in visible pricing: if Stripe showed "10€ VAT included", in Polar the customer will see "10€ + VAT" because Polar calculates it. Either drop the net price or raise the visible one. Communicate it.

3. Refunds and disputes: the logic is different. Read Polar's docs before processing your first refund.

Bottom line

Migrating Stripe → Polar is ~2 hours of code if you have the abstraction in place, or ~1 day from scratch. The longest part is testing in sandbox and shadow-deploying.

In return: you forget about VAT, about OSS filings, about the accountant arguing what kind of service a SaaS is. If you sell to Europe, it's worth it.