# Webhook Notifications

> Receive real-time payment and payout status updates via HMAC-signed webhooks.

The 2328.io system sends a webhook to your `url_callback` whenever a payment status changes. This is the recommended way to get notified about successful payments.

## Request format

- **Method:** `POST`
- **Content-Type:** `application/json`
- **Signature:** `sign` field in the request body

## Payload

The webhook body follows the `/v1/payment/info` response and adds `tx_explorer_url` plus the `sign` field used for signature verification.

### Successful payment

```json
{
  "uuid": "db17d490-15b6-47b9-9015-91d1d8b119f2",
  "order_id": "ORDER-12345",
  "amount": "180.00000000",
  "currency": "RUB",
  "url": "https://go.2328.io/db17d490-15b6-47b9-9015-91d1d8b119f2",
  "expires_at": "2026-05-09T16:56:58+03:00",
  "created_at": "2026-05-09T15:56:58+03:00",
  "payer_currency": "TON",
  "payer_amount": "0.95256917",
  "network": "TON",
  "address": "UQA0RevhkCQx-EltyNgPPeG8dqtnCz7ZslOzMdNQlLxVaNBb",
  "payment_status": "paid",
  "txid": "41c2a327323480af8e705d05deb09c238a41779928832abef4bb77c862357b11",
  "tx_explorer_url": "https://tonviewer.com/transaction/41c2a327323480af8e705d05deb09c238a41779928832abef4bb77c862357b11",
  "payment_amount": "0.95256917",
  "merchant_amount": "0.949711462490000000",
  "amount_usd": "2.41324380",
  "exchange_rate": "0.01340691",
  "sign": "6f8c15b6e53b506d5bfa38ed3fb3b50697af73434262153c02e412541372f04d"
}
```

### Cancelled / failed payment

When the payment is not in a terminal `paid` state, `txid`, `payment_amount`, and `merchant_amount` are `null`:

```json
{
  "uuid": "48edaf2d-2c49-4638-8f86-88636f661c1f",
  "order_id": "ORDER-12345",
  "amount": "2800.00000000",
  "currency": "RUB",
  "url": "https://go.2328.io/48edaf2d-2c49-4638-8f86-88636f661c1f",
  "expires_at": "2026-05-09T06:19:04+03:00",
  "created_at": "2026-05-09T05:19:04+03:00",
  "payer_currency": "ETH",
  "payer_amount": "0.01620968",
  "network": "ETH-ERC20",
  "address": "0x37c20d6d96d130Bc5B33D832e43b8e16aACe0c59",
  "payment_status": "cancel",
  "txid": null,
  "tx_explorer_url": null,
  "payment_amount": null,
  "merchant_amount": null,
  "amount_usd": "37.53934800",
  "exchange_rate": "0.01340691",
  "sign": "40ce68ad9691ad54e684329d75ab5adaf5b01409a2d18d3e0110b8c1be605342"
}
```

### Field reference

| Field | Type | Description |
|-------|------|-------------|
| `uuid` | string | Payment UUID |
| `order_id` | string | Your order ID |
| `amount` | decimal (8 dp) | Fiat amount in `currency` |
| `currency` | string | Fiat currency the merchant requested |
| `url` | string | Hosted checkout URL |
| `expires_at` | string (ISO 8601) | When the payment session expires |
| `created_at` | string (ISO 8601) | When the payment session was created |
| `payer_currency` | string | Crypto the payer is paying in |
| `payer_amount` | decimal (8 dp) | Amount of crypto expected |
| `network` | string | Blockchain network |
| `address` | string | Deposit address |
| `payment_status` | string | One of: `pending`, `check`, `paid`, `underpaid_check`, `underpaid`, `overpaid`, `cancel`, `aml_lock` (see [References](/docs/references)) |
| `txid` | string \| null | Blockchain tx hash, present only after a confirmed payment |
| `tx_explorer_url` | string \| null | Blockchain explorer transaction URL. `null` when `txid` is absent or the transfer is internal P2P. |
| `payment_amount` | decimal \| null | Actual paid amount, present only after payment |
| `merchant_amount` | decimal (18 dp) \| null | Amount credited to merchant after fees |
| `amount_usd` | decimal (8 dp) | Amount in USD at the time of creation |
| `exchange_rate` | decimal | Crypto / fiat exchange rate used |
| `sign` | string (hex) | HMAC-SHA256 signature of the payload |

## Verifying the signature

To verify a webhook signature:

1. Extract the `sign` field from the payload
2. Remove the `sign` field from the object
3. Encode the remaining fields as JSON
4. Encode the JSON in Base64
5. Compute HMAC-SHA256 from the Base64 string using your API_KEY
6. Compare the computed signature with the `sign` value using a constant-time comparison

#### php

```php
<?php
function verifyWebhookSign(array $data, string $apiKey): bool {
    $receivedSign = $data['sign'] ?? '';
    unset($data['sign']);

    $json = json_encode($data, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
    $base64 = base64_encode($json);
    $calculated = hash_hmac('sha256', $base64, $apiKey);

    return hash_equals($calculated, $receivedSign);
}

$apiKey = 'YOUR_API_KEY';
$payload = json_decode(file_get_contents('php://input'), true);

if (!verifyWebhookSign($payload, $apiKey)) {
    http_response_code(401);
    exit;
}

switch ($payload['payment_status']) {
    case 'paid':
    case 'overpaid':
        // Credit the order — check idempotency by order_id first
        break;
    case 'underpaid_check':
    case 'underpaid':
    case 'cancel':
        break;
}

http_response_code(200);
```

#### js

```js
import crypto from "crypto";
import express from "express";

const app = express();
app.use(express.json());

function verifyWebhookSign(payload, apiKey) {
  const { sign, ...rest } = payload;
  const json = JSON.stringify(rest);
  const base64 = Buffer.from(json).toString("base64");
  const calculated = crypto
    .createHmac("sha256", apiKey)
    .update(base64)
    .digest("hex");
  return crypto.timingSafeEqual(
    Buffer.from(calculated),
    Buffer.from(sign || ""),
  );
}

app.post("/webhook", (req, res) => {
  if (!verifyWebhookSign(req.body, process.env.API_KEY)) {
    return res.sendStatus(401);
  }

  const { order_id, payment_status, txid } = req.body;

  if (payment_status === "paid" || payment_status === "overpaid") {
    // Credit the order — check idempotency by order_id first
  }

  res.sendStatus(200);
});
```

#### python

```python
import json
import hmac
import hashlib
import base64
from fastapi import FastAPI, Request, HTTPException

app = FastAPI()
API_KEY = "YOUR_API_KEY"

def verify_webhook_sign(payload: dict, api_key: str) -> bool:
    received = payload.pop("sign", "")
    body = json.dumps(payload, separators=(",", ":"), ensure_ascii=False)
    b64 = base64.b64encode(body.encode("utf-8")).decode()
    calculated = hmac.new(api_key.encode(), b64.encode(), hashlib.sha256).hexdigest()
    return hmac.compare_digest(calculated, received)

@app.post("/webhook")
async def webhook(request: Request):
    payload = await request.json()
    if not verify_webhook_sign(payload, API_KEY):
        raise HTTPException(401)

    if payload["payment_status"] in ("paid", "overpaid"):
        # Credit the order — check idempotency by order_id first
        pass

    return {"ok": True}
```

#### go

```go
package main

import (
    "bytes"
    "crypto/hmac"
    "crypto/sha256"
    "encoding/base64"
    "encoding/hex"
    "encoding/json"
    "io"
    "net/http"
)

func verifyWebhookSign(body []byte, apiKey string) (map[string]any, bool) {
    var payload map[string]any
    if err := json.Unmarshal(body, &payload); err != nil {
        return nil, false
    }
    received, _ := payload["sign"].(string)
    delete(payload, "sign")

    var buf bytes.Buffer
    enc := json.NewEncoder(&buf)
    enc.SetEscapeHTML(false)
    enc.Encode(payload)
    reencoded := bytes.TrimRight(buf.Bytes(), "\n")

    b64 := base64.StdEncoding.EncodeToString(reencoded)
    h := hmac.New(sha256.New, []byte(apiKey))
    h.Write([]byte(b64))
    calculated := hex.EncodeToString(h.Sum(nil))

    return payload, hmac.Equal([]byte(calculated), []byte(received))
}

func webhookHandler(w http.ResponseWriter, r *http.Request) {
    body, _ := io.ReadAll(r.Body)
    payload, ok := verifyWebhookSign(body, apiKey)
    if !ok {
        http.Error(w, "invalid signature", http.StatusUnauthorized)
        return
    }

    status, _ := payload["payment_status"].(string)
    if status == "paid" || status == "overpaid" {
        // Credit the order — check idempotency first
    }
    w.WriteHeader(http.StatusOK)
}
```

#### ruby

```ruby
require "json"
require "openssl"
require "base64"
require "sinatra"

API_KEY = "YOUR_API_KEY"

def verify_webhook_sign(payload, api_key)
  received = payload.delete("sign") || ""
  body = payload.to_json
  b64 = Base64.strict_encode64(body)
  calculated = OpenSSL::HMAC.hexdigest("SHA256", api_key, b64)
  OpenSSL.fixed_length_secure_compare(calculated, received)
end

post "/webhook" do
  payload = JSON.parse(request.body.read)
  halt 401 unless verify_webhook_sign(payload, API_KEY)

  if %w[paid overpaid].include?(payload["payment_status"])
    # Credit the order — check idempotency by order_id first
  end

  status 200
end
```

> **DANGER:** **Always verify the signature** before crediting any funds to a user. An unsigned or incorrectly-signed webhook could be a spoofed request.

## Payout webhooks

When a payout's `status` changes, the system sends a `POST` webhook to the `url_callback` URL passed when the payout was created. If `url_callback` was not provided, no webhooks are sent for that payout.

> **WARNING:** Payout webhooks must be verified with your **Payout API key** — not the regular API key. The signing algorithm is identical to payment webhooks (strip `sign`, JSON-encode, base64, HMAC-SHA256), only the key differs.

### Payload

```json
{
  "uuid": "019dff1f-0dbd-7277-8d45-271e7775388f",
  "order_id": "4dfdcc84402b1185b71cbe399321533e",
  "status": "completed",
  "currency": "TRX",
  "network": "TRX-TRC20",
  "amount": "3.00",
  "merchant_amount": "3.00",
  "network_amount": "3.00",
  "amount_usd": "1.04",
  "to_address": "THauRv5tcucQRohXg8NiyGTk16DX1XQG5x",
  "memo": null,
  "txid": "9242e533703704ef3eaba840f70b4a26333e72c943377ee375fea17badb53def",
  "tx_explorer_url": "https://tronscan.org/#/transaction/9242e533703704ef3eaba840f70b4a26333e72c943377ee375fea17badb53def",
  "block_number": null,
  "error_type": null,
  "created_at": "2026-05-07T00:08:38+03:00",
  "updated_at": "2026-05-07T00:08:54+03:00",
  "from_currency": "USDT",
  "debited_amount": "1.050735",
  "debited_currency": "USDT",
  "sign": "925ad7bf3d6841864101f7cc2c7e30652e70a06cdb04dbe07a0129480000ce4a"
}
```

### Field reference

| Field | Type | Description |
|-------|------|-------------|
| `uuid` | string | Payout UUID |
| `order_id` | string | Your idempotency / reference ID, if you provided one |
| `status` | string | `pending`, `completed`, `failed`, `cancelled` (see [References](/docs/references)) |
| `currency` | string | Withdrawal currency |
| `network` | string | Blockchain network |
| `amount` | decimal | Withdrawal amount (in `currency`) |
| `merchant_amount` | decimal | Amount charged from the merchant balance |
| `network_amount` | decimal | Amount actually sent on-chain |
| `amount_usd` | decimal | USD value at the time of the payout |
| `to_address` | string | Recipient blockchain address |
| `memo` | string \| null | Memo / destination tag, if used |
| `txid` | string \| null | Blockchain transaction hash, set on `completed` |
| `tx_explorer_url` | string \| null | Blockchain explorer transaction URL. `null` when `txid` is absent or the transfer is internal P2P. |
| `block_number` | integer \| null | Block height of the on-chain transaction |
| `error_type` | string \| null | Reason when `status = failed` (e.g. `aml_risk`, see [References](/docs/references)) |
| `created_at` | string (ISO 8601) | When the payout was created |
| `updated_at` | string (ISO 8601) | When the status last changed |
| `from_currency` | string | Source balance the payout was debited from when auto-conversion was used (e.g. `USDT` for a `BTC` payout) |
| `debited_amount` | decimal | Amount debited from `from_currency` balance |
| `debited_currency` | string | Currency of the debit |
| `sign` | string (hex) | HMAC-SHA256 signature of the payload, signed with the **Payout API key** |

## Best practices

- **Idempotency** — Always check if the payment has already been processed (by `order_id` or `uuid`). Webhooks may arrive multiple times.
- **Fast response** — Return HTTP 200 as quickly as possible. Offload heavy work to a background queue.
- **Retries** — If the system doesn't receive an HTTP 200, the webhook is resent after 2 minutes. Maximum 5 retry attempts.
- **Async processing** — Handle webhook events asynchronously to avoid blocking the response.
- **Security** — ALWAYS verify the `sign` signature before trusting the payload.

> **WARNING:** Webhooks can arrive out of order. Don't assume the first webhook you receive is the final state — always re-fetch via `/v1/payment/info` (or `/v1/payout/status/{uuid}`) if you need certainty.

## Delivery and processing contract

Use the following order inside your webhook endpoint:

1. Read the request body without logging secrets or the full signature.
2. Identify whether it is a payment/static-wallet event or a payout event so you select the correct API key.
3. Remove `sign`, reproduce the documented JSON bytes, calculate HMAC-SHA256, and compare in constant time.
4. Validate required identifiers, decimal strings, and status values.
5. Atomically insert an inbox/idempotency record. If it already exists, return HTTP 200 without repeating side effects.
6. Commit the order/ledger mutation and enqueue non-critical email, analytics, or notifications.
7. Return HTTP 200 quickly.

Do not call slow third-party services while holding the idempotency transaction. A timeout after you commit but before returning can cause a retry; the duplicate must observe the committed inbox key and become a no-op.

### Recommended idempotency keys

| Event | Primary identity | Notes |
|-------|------------------|-------|
| Payment session | `uuid` + status/version evidence | The same invoice can emit multiple legitimate status changes. |
| Partial-payment top-up | invoice `uuid` + `txid` | More than one transfer can belong to the same underpaid invoice. |
| Static-wallet deposit | network + `txid` | `order_id` is reused by every deposit to that wallet. |
| Payout | payout `uuid` + status | Never create a second payout from webhook retry logic. |

If your schema has no event id, store the verified payload hash as additional audit evidence, but do not replace the business identities above with a timestamp.

## Ordering and reconciliation

Delivery is at-least-once and status messages can race. Implement monotonic business rules rather than “last request wins”:

- never move a fulfilled order back to `check` because an older event arrived late;
- allow `underpaid_check` to receive additional txids without repeating earlier credits;
- treat `paid` and `overpaid` as successful settlement states, while preserving their different amounts;
- keep `underpaid` as a final partial-payment outcome unless the authoritative API later reports another state;
- route `aml_lock` to review and do not let a generic retry worker fulfill it;
- query payment/payout info whenever the transition is impossible, missing context, or financially ambiguous.

Run scheduled reconciliation even when webhook delivery appears healthy. Compare your local terminal state and credited amount with `/v1/payment/info`, `/v1/static-wallet/transactions`, or `/v1/payout/status/{uuid}` and alert on differences instead of silently overwriting ledger history.

## Webhook endpoint security

- Require HTTPS and keep the callback publicly reachable; private/loopback callback targets are rejected during payment creation.
- Enforce a small request-body limit and JSON content type.
- Rate-limit before expensive work, but leave enough headroom for legitimate bursts and retries.
- Never authorize a webhook by source IP alone. Network allowlists are defense in depth; HMAC verification is mandatory.
- Redact `sign`, API keys, addresses when required by policy, and personal metadata from application logs.
- Keep both current and explicitly scheduled replacement keys available during a controlled rotation window; never guess which key signed an event.
- Return a generic error body on invalid signatures so the endpoint does not become a key or account oracle.