Checkout

A Checkout is a request or session that tells SumUp to collect a specific amount in a specific currency. It connects the commercial intent represented by a Sale with payment processing.

A Checkout commonly contains:

• The amount and currency to collect
• The merchant receiving the payment
• A merchant-defined reference
• Optional customer, expiration, redirect, and callback details
• Its current status and any linked Transactions

A Checkout is not proof that payment succeeded. It can exist before any payment attempt and can remain PENDING, fail, or expire without a successful Transaction.

Checkout Types in the Public APIs

The Developer Portal uses Checkout in two related payment flows:

• The Checkouts API creates an online Checkout, processes it with a payment instrument, and retrieves its latest state. Start with Create a checkout, then use a supported integration such as the Payment Widget or Hosted Checkout.
• The Readers API creates a Checkout on a paired card reader. This starts an asynchronous in-person payment flow. See Create a Reader Checkout.

These resources have different endpoint shapes and lifecycles, but serve the same conceptual purpose: they coordinate how a payment should be attempted.

Typical Online Checkout Flow

sequenceDiagram
    autonumber
    participant App as Your backend
    participant API as Checkouts API
    participant UI as Payment UI
    participant Tx as Transaction record

    App->>API: Create checkout
    API-->>App: Checkout with PENDING status
    App->>UI: Provide checkout ID
    UI->>API: Process payment
    API->>Tx: Record payment attempt
    API-->>UI: Return result or next action
    App->>API: Retrieve checkout
    API-->>App: Latest status and linked transactions

For redirect-based payment methods or 3DS, processing can return a next action instead of a final result. Always use Retrieve a checkout from your backend to confirm the latest Checkout status.

Relationship to a Sale and Transaction

• The Sale describes the items, taxes, discounts, customer, and other commercial context.
• The Checkout carries the amount, currency, and instructions needed to attempt payment.
• Processing the Checkout creates or updates a Transaction, which records the financial result.

A newly created Checkout can have an empty transactions array. Payment processing attaches Transaction records as attempts occur. Use the Checkout to manage the payment flow; use the Transactions API for transaction details, history, and post-payment operations.