# Polar Checkout API (https://talivia.com/docs/revenue-guides/polar/checkout-api)



This is the most reliable Polar integration. Talivia receives the same session ID in the signed `order.paid` webhook and can attribute the order without depending on a return visit.

## Send the Talivia session to your backend [#send-the-talivia-session-to-your-backend]

```javascript title="Browser checkout handoff"
const sessionId = window.talivia.getSessionId();

const response = await fetch('/api/create-polar-checkout', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ sessionId }),
});

const { url } = await response.json();
window.location.assign(url);
```

The session ID is an attribution identifier, not authentication. Validate the product and signed-in user on your backend as usual.

## Add metadata when checkout is created [#add-metadata-when-checkout-is-created]

Keep the Polar access token on the server. Polar copies checkout metadata to the resulting order and subscription, so one field covers both one-time and recurring products.

```javascript title="Create a Polar Checkout Session"
import { Polar } from '@polar-sh/sdk';

const polar = new Polar({
  accessToken: process.env.POLAR_ACCESS_TOKEN,
});

const checkout = await polar.checkouts.create({
  products: [process.env.POLAR_PRODUCT_ID],
  successUrl:
    'https://your-site.com/thanks?checkout_id={CHECKOUT_ID}',
  returnUrl: 'https://your-site.com/pricing',
  externalCustomerId: user.id,
  customerEmail: user.email,
  metadata: {
    talivia_session_id: sessionId,
  },
});

return Response.json({ url: checkout.url });
```

`externalCustomerId` should be a stable ID from your own application. It gives Talivia a second matching signal for future renewals. Keep `checkout_id={CHECKOUT_ID}` in the success URL as a useful fallback and debugging signal.