adyen-webhooks

Adyen Webhooks

When to Use This Skill

• How do I receive Adyen webhooks (standard notifications)?
• How do I verify Adyen webhook HMAC signatures?
• How do I handle AUTHORISATION, CAPTURE, REFUND, or CHARGEBACK events?
• Why is my Adyen HMAC signature verification failing?
• What response body does Adyen expect from my webhook endpoint?

How Adyen Webhooks Work

Adyen sends standard notifications as an HTTP POST with a JSON body containing a batch of notificationItems. Each item wraps a NotificationRequestItem:

{
  "live": "false",
  "notificationItems": [
    {
      "NotificationRequestItem": {
        "eventCode": "AUTHORISATION",
        "success": "true",
        "pspReference": "7914073381342284",
        "merchantAccountCode": "TestMerchant",
        "merchantReference": "TestPayment-1407325143704",
        "amount": { "value": 1130, "currency": "EUR" },
        "additionalData": { "hmacSignature": "coqCmt/IZ4E3CzPvMY8zTjQVL5hYJUiBRg8UU+iCWo0=" }
      }
    }
  ]
}

Your endpoint must:

1. Verify the HMAC signature on each item (additionalData.hmacSignature).
2. Acknowledge with the literal body [accepted] and HTTP 200 — otherwise Adyen retries.

Verification (core)

Adyen's HMAC is not computed over the raw request body. It is computed over a :-delimited string of specific fields, in this exact order:

pspReference : originalReference : merchantAccountCode : merchantReference : amount.value : amount.currency : eventCode : success

Each field value is escaped (\ → \\, : → \:), empty fields become empty strings, and the HMAC key from the Customer Area is a hex string that must be hex-decoded before use. The result is HMAC-SHA256, base64-encoded, and compared against additionalData.hmacSignature. Because the signature covers parsed fields, you parse the JSON first, then verify each item.

The official @adyen/api-library SDK does all of this for you:

const { hmacValidator } = require('@adyen/api-library');

const validator = new hmacValidator();

// item = notificationItems[i].NotificationRequestItem (plain parsed object)
// ADYEN_HMAC_KEY = hex string from the Customer Area
const valid = validator.validateHMAC(item, process.env.ADYEN_HMAC_KEY);
// reads item.additionalData.hmacSignature and compares (timing-safe) internally