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A checkout session represents one buyer’s attempt to pay you through the Slash hosted checkout. It is the buyer-facing wrapper around a payment intent: the session carries the hosted url, the expiry window, and page configuration, while the payment intent inside it tracks the money. Create one session per buyer checkout with POST /checkout-session and mount its url with the @slashfi/checkout-js SDK. Treat the url as single-use — mint a fresh session each time a buyer reaches your checkout rather than reusing one across buyers.

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Statuses

A session’s status is derived from its payment intent: it is complete exactly when the intent is succeeded. A payment that is in flight when the expiry passes still settles — an open session with a processing intent stays open until the payment resolves.

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Idempotency and expiry

  • POST /checkout-session requires an X-Idempotency-Key header, unique per session you intend to create. Retrying with the same key returns the existing session; reusing a key with different parameters is rejected with a 400.
  • expiresAt defaults to 24 hours after creation and must be between 30 minutes and 7 days out.

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Metadata

customMetadata is echoed back on reads and on the checkout_session.completed webhook — use it to carry your own order reference (for example { "orderId": "ord_123" }) so fulfillment can correlate the webhook to the right order without extra lookups.

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Payment methods

Card payments are always enabled. Apple Pay and Google Pay are enabled by default and can be disabled per session from your backend with config.paymentMethods, for example { "paymentMethods": { "applePay": false } } inside config.

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Updating a session

While a session is open you can change its amount, expiry, or page configuration with PATCH /checkout-session/{id}. Send only the fields you want to change. The session keeps its id and hosted url, so a buyer who already has the checkout open picks up the new amount in place. Updates only apply to open sessions. Once the buyer’s payment is in flight the update is rejected with 409, and complete or expired sessions cannot be updated at all.

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Fulfillment

Fulfill from the checkout_session.completed webhook, or poll GET /checkout-session/{id} and check for status: "complete". The SDK’s onComplete callback is a browser signal for updating the UI — never grant goods or services on it alone.