Webhook

Add webhook endpoints in the dashboard (under Developer) — up to five per mode, each with its own URL, name and signing secret, so a store and an ERP can each receive their own copy. When a payment is confirmed, we send a POST to every endpoint that is switched on, with this payload:

{
  "id": "evt_...",
  "type": "payment.paid",
  "livemode": false,
  "created_at": "2026-08-11T12:05:00+07:00",
  "data": {
    "payment_request_id": "payreq_9b2f...",
    "external_id": "ORD-1234",
    "merchant_ref": "INV-2026-001",
    "amount": 150000,
    "currency": "IDR",
    "customer": { "name": "Budi", "email": "budi@toko.dev" },
    "paid_at": "2026-08-11T12:04:58+07:00"
  }
}

Delivery is at-least-once: the same event may arrive more than once and always carries the same id — dedupe by id. With several endpoints, each receives the event once and retries on its own: one endpoint rejecting it never delays another. Your endpoint must answer 2xx; otherwise we retry with exponential backoff for up to 7 attempts over ±33 hours. The webhook URL must be https and point to a public address. Live and test are separate endpoints with separate signing secrets: configure each in its own dashboard mode. A test-mode event only ever reaches the test endpoint and carries livemode: false; a live one only reaches the live endpoint. A test secret never verifies a live payload.

Verify the signature

Every delivery carries a timestamped signature in the Kasera-Signature-V1 header: t=<unix>,v1=<hex>, where v1 is HMAC-SHA256 over t + "." + rawBody. Verify against t and reject deliveries whose timestamp is more than 5 minutes off your clock — that is what stops a captured delivery from being replayed later. After a secret rotation the header carries two v1 entries for 24 hours — one per secret — so accept the delivery if any entry matches. The event id is also in Kasera-Event-Id.

// Node.js
const crypto = require("crypto");

// Kasera-Signature-V1: t=1723350300,v1=5f4d...[,v1=9a1b...]
function verify(rawBody, v1Header, secret, toleranceSeconds = 300) {
  const parts = v1Header.split(",");
  const t = Number(parts[0].slice(2)); // "t=<unix>"
  if (!Number.isFinite(t)) return false;
  if (Math.abs(Date.now() / 1000 - t) > toleranceSeconds) return false;
  const expected = crypto
    .createHmac("sha256", secret)
    .update(t + "." + rawBody)
    .digest("hex");
  return parts
    .slice(1)
    .filter((p) => p.startsWith("v1="))
    .some((p) => {
      const sig = Buffer.from(p.slice(3));
      return (
        sig.length === expected.length &&
        crypto.timingSafeEqual(sig, Buffer.from(expected))
      );
    });
}

Legacy header (deprecated)

Deliveries still carry the original Kasera-Signature header — bare hex HMAC-SHA256 over the raw body, no timestamp — so existing verifiers keep working unchanged. It is deprecated: it cannot protect against replay, and it is signed with the current secret only (no rotation grace). Migrate to Kasera-Signature-V1; the legacy header will be removed after a deprecation period announced in advance.

// Node.js — legacy Kasera-Signature (deprecated)
const crypto = require("crypto");

function verifyLegacy(rawBody, signatureHeader, secret) {
  const expected = crypto
    .createHmac("sha256", secret)
    .update(rawBody)
    .digest("hex");
  return crypto.timingSafeEqual(
    Buffer.from(signatureHeader),
    Buffer.from(expected)
  );
}

The secret is visible in the dashboard whenever you need it, and it changes only when you rotate it — moving the webhook URL to a new domain keeps the same secret, so a migration needs no redeploy of your verification code. Rotation has a 24-hour grace window: the old secret keeps signing a second v1 entry alongside the new one, so deploy the new secret at your own pace — in-flight retries keep verifying throughout. You can also add an endpoint without a URL to get its secret first: build and deploy the handler, point the domain at us afterwards. Switching an endpoint off parks its events without burning retries until you switch it back on.