Webhooks

Inzi sends webhooks to your server when payment events occur. This is the primary way to know when a checkout is paid, expired, or underpaid.

Events

Partial payments (top-up)

If a customer sends less than the required amount, Inzi sends a checkout.underpaid webhook. The checkout stays active — the customer can send additional transfers to the same deposit address to cover the difference.

Inzi accumulates all transfers automatically. When the total reaches the expected amount (within tolerance), a checkout.completed webhook fires.

Customer sends 60 USDT (expected: 100 USDT)
  → checkout.underpaid webhook (amount_crypto: "60")

Customer sends 40 USDT to the same address
  → checkout.completed webhook (amount_crypto: "100")

Important for your handler:

• Do not credit the user on checkout.underpaid — wait for checkout.completed
• If you need to show progress, use the amount_crypto field from the underpaid webhook
• The checkout still expires at expires_at — partial payments must be completed before then
• After checkout.completed, no further webhooks are sent for that checkout

Webhook payload

Every webhook is an HTTP POST to your webhook_url:

{
  "event": "checkout.completed",
  "checkout_id": "chk_live_abc123def456",
  "merchant_id": "mrc_xxxxx",
  "data": {
    "status": "completed",
    "amount": "25.00",
    "currency": "USD",
    "payment": {
      "amount_crypto": "25.000000",
      "crypto_currency": "USDT",
      "network": "ton",
      "tx_hash": "abc123...",
      "sender_address": "UQ...",
      "confirmed_at": "2026-04-04T12:05:00Z"
    },
    "metadata": {
      "order_id": "uuid-xxx",
      "user_id": "uuid-yyy"
    }
  },
  "created_at": "2026-04-04T12:05:01Z"
}

The metadata object is exactly what you passed when creating the checkout — Inzi never reads or modifies it.

Signature verification

Every webhook includes these headers:

How to verify

1. Build the signed payload: {timestamp}.{raw_body}
2. Compute HMAC-SHA256 using your webhook secret
3. Compare signatures (timing-safe)
4. Reject if timestamp is older than 5 minutes

import crypto from 'crypto'
 
function verifyWebhook(rawBody, headers, webhookSecret) {
  const timestamp = headers['x-inzi-timestamp']
  const signature = headers['x-inzi-signature'].replace('sha256=', '')
 
  // 1. Build signed payload
  const signedPayload = `${timestamp}.${rawBody}`
 
  // 2. Compute expected signature
  const expected = crypto
    .createHmac('sha256', webhookSecret)
    .update(signedPayload)
    .digest('hex')
 
  // 3. Timing-safe comparison
  if (!crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(signature))) {
    throw new Error('Invalid webhook signature')
  }
 
  // 4. Check timestamp freshness
  if (Math.abs(Date.now() / 1000 - parseInt(timestamp)) > 300) {
    throw new Error('Webhook timestamp too old')
  }
 
  return JSON.parse(rawBody)
}

import hmac, hashlib, time, json
 
def verify_webhook(body: str, headers: dict, secret: str) -> dict:
    timestamp = headers["X-Inzi-Timestamp"]
    signature = headers["X-Inzi-Signature"].removeprefix("sha256=")
 
    signed_payload = f"{timestamp}.{body}"
    expected = hmac.new(
        secret.encode(), signed_payload.encode(), hashlib.sha256
    ).hexdigest()
 
    if not hmac.compare_digest(expected, signature):
        raise ValueError("Invalid webhook signature")
 
    if abs(time.time() - int(timestamp)) > 300:
        raise ValueError("Webhook too old")
 
    return json.loads(body)

Retry policy

If your endpoint returns a non-2xx status code, Inzi retries with exponential backoff:

Each retry sends the same X-Inzi-Webhook-Id. Use this to deduplicate.

After 5 failed attempts, the webhook is marked as failed. You can manually retry from the merchant dashboard .

Idempotency

Your webhook handler must handle duplicate deliveries:

• Use checkout_id as the idempotency key
• If already processed, return 200 OK without re-processing
• Inzi may retry even after receiving a 200 (network ambiguity)

app.post('/webhooks/inzi', async (req, res) => {
  const event = verifyWebhook(req.rawBody, req.headers, WEBHOOK_SECRET)
 
  // Deduplicate
  if (await isAlreadyProcessed(event.checkout_id)) {
    return res.status(200).json({ ok: true })
  }
 
  if (event.event === 'checkout.completed') {
    await fulfillOrder(event.data.metadata.order_id)
    await markAsProcessed(event.checkout_id)
  }
 
  res.status(200).json({ ok: true })
})

Test mode webhooks

When using sk_test_ keys, a mock checkout.completed webhook fires 5 seconds after checkout creation. No real blockchain transaction occurs.

The test webhook payload includes "test": true and uses chk_test_ prefixed IDs.

This lets you test your entire integration flow without testnet tokens.

Polling fallback

If webhook delivery fails, you can poll for status:

curl https://api.inzilink.com/api/v1/checkouts/chk_live_abc123 \
  -H "Authorization: Bearer sk_live_xxxxx"

Poll every 3-5 seconds until status is completed or expired. See Get Checkout.