Use the Adyen Checkout API to build a Drop-in integration and handle payment result codes

Steps

1. On the server side, POST to /v70/sessions (or versioned equivalent) with amount, currency, merchantAccount, returnUrl, and a reference to create a payment session; return the sessionId and sessionData to the frontend
2. On the frontend, import the Adyen Web Drop-in component from the CDN or npm package, instantiate AdyenCheckout with the sessionId, sessionData, and clientKey, then call create('dropin').mount('#container')
3. The Drop-in handles payment method rendering, 3DS2 challenges, and redirect flows automatically; no additional frontend payment-method-specific code is needed for the Sessions flow
4. On your returnUrl page, finalise the payment by reading the redirectResult query parameter (present for redirect-based methods) and calling POST /v70/sessions/{sessionId}/result or letting the Drop-in handle it via the onPaymentCompleted callback
5. Map the resultCode in the response: Authorised means success; Refused, Error, and Cancelled each require different customer-facing messaging; Pending and Received are used for delayed-capture methods like bank transfers