# Quick start

A minimal payment integration: creating an invoice via the API and handling the payment notification. The final section covers order fulfillment. The examples are self-contained; no SDK is used.

:::tip
**Working with an AI agent?** Give it the [markdown version of this page](/quick-start.md). It has enough detail to build an integration for your site or store.
:::

## Prerequisites

| Value | Where to get it |
| --- | --- |
| API key | The [Integrations](https://dash.bitsby.app/integrations/list) section |
| Project ID | The [Projects](https://dash.bitsby.app/projects/list) section |
| Webhook secret | Project settings |

In the same project settings, set the **Webhook URL**—the address of the notification handler on your server. HTTPS only; redirects are not followed.

The examples use test values—replace them with your own.

## Creating an invoice

`POST https://api.bitsby.app/invoices/create`, the API key is passed in the `Authorization` header.

| Parameter | Required | Value |
| --- | --- | --- |
| `projectId` | yes | Project ID, UUID |
| `amountFiat` | yes | Invoice amount |
| `currencyFiat` | yes | Currency: USD, EUR, RUB |
| `timeToPay` | yes | Payment deadline in hours: 0.5, 1, 3, 6, 12 |
| `description` | no | Description, shown to the customer on the payment page |
| `serviceData` | no | Service data, not shown to the customer. We recommend passing the order number: it comes back in the payment notification |

**cURL**

```bash showLineNumbers
curl -X POST https://api.bitsby.app/invoices/create \
  -H "Authorization: Token MSvL2ltaDZdWVjmZURURMVWhqSJLT2NURjhL2Fla1Z1T1IxQTltKs1T3Ay" \
  -F "projectId=9deea1e2-0c08-41a3-bdc2-a34eada3892d" \
  -F "amountFiat=49.90" \
  -F "currencyFiat=USD" \
  -F "timeToPay=1" \
  -F "description=Order 4172" \
  -F "serviceData=order-4172"
```

**PHP**

```php showLineNumbers
<?php
$apiKey    = 'MSvL2ltaDZdWVjmZURURMVWhqSJLT2NURjhL2Fla1Z1T1IxQTltKs1T3Ay';
$projectId = '9deea1e2-0c08-41a3-bdc2-a34eada3892d';

$ch = curl_init('https://api.bitsby.app/invoices/create');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT        => 10,
    CURLOPT_HTTPHEADER     => ['Authorization: Token '.$apiKey],
    CURLOPT_POSTFIELDS     => http_build_query([
        'projectId'    => $projectId,
        'amountFiat'   => 49.90,
        'currencyFiat' => 'USD',
        'timeToPay'    => 1,
        'description'  => 'Order 4172',
        'serviceData'  => 'order-4172',  // your order id
    ]),
]);

$response = json_decode(curl_exec($ch), true);
curl_close($ch);

if ($response['result'] !== 'success') {
    exit('API error: '.$response['data']);
}

$invoice = $response['data'];

// $invoice['id']  — invoice id, store it with the order
// $invoice['url'] — payment page for the customer
```

**TypeScript**

```typescript showLineNumbers
const API_KEY = 'MSvL2ltaDZdWVjmZURURMVWhqSJLT2NURjhL2Fla1Z1T1IxQTltKs1T3Ay';
const PROJECT_ID = '9deea1e2-0c08-41a3-bdc2-a34eada3892d';

interface Invoice {
    id: string;
    uid: string;
    url: string;
    timeToPayDatetime: string;
}

const response = await fetch('https://api.bitsby.app/invoices/create', {
    method: 'POST',
    headers: { Authorization: `Token ${API_KEY}` },
    body: new URLSearchParams({
        projectId: PROJECT_ID,
        amountFiat: '49.90',
        currencyFiat: 'USD',
        timeToPay: '1',
        description: 'Order 4172',
        serviceData: 'order-4172',  // your order id
    }),
    signal: AbortSignal.timeout(10_000),
});

const result: { result: string; data: Invoice | string } = await response.json();

if (result.result !== 'success') {
    throw new Error(`API error: ${result.data}`);
}

const invoice = result.data as Invoice;

// invoice.id  — invoice id, store it with the order
// invoice.url — payment page for the customer
```

**JavaScript**

```js showLineNumbers
const API_KEY = 'MSvL2ltaDZdWVjmZURURMVWhqSJLT2NURjhL2Fla1Z1T1IxQTltKs1T3Ay';
const PROJECT_ID = '9deea1e2-0c08-41a3-bdc2-a34eada3892d';

const response = await fetch('https://api.bitsby.app/invoices/create', {
    method: 'POST',
    headers: { Authorization: `Token ${API_KEY}` },
    body: new URLSearchParams({
        projectId: PROJECT_ID,
        amountFiat: '49.90',
        currencyFiat: 'USD',
        timeToPay: '1',
        description: 'Order 4172',
        serviceData: 'order-4172',  // your order id
    }),
    signal: AbortSignal.timeout(10_000),
});

const result = await response.json();

if (result.result !== 'success') {
    throw new Error(`API error: ${result.data}`);
}

const invoice = result.data;

// invoice.id  — invoice id, store it with the order
// invoice.url — payment page for the customer
```

**Python**

```python showLineNumbers
import requests

API_KEY = 'MSvL2ltaDZdWVjmZURURMVWhqSJLT2NURjhL2Fla1Z1T1IxQTltKs1T3Ay'
PROJECT_ID = '9deea1e2-0c08-41a3-bdc2-a34eada3892d'

response = requests.post(
    'https://api.bitsby.app/invoices/create',
    headers={'Authorization': f'Token {API_KEY}'},
    data={
        'projectId': PROJECT_ID,
        'amountFiat': '49.90',
        'currencyFiat': 'USD',
        'timeToPay': '1',
        'description': 'Order 4172',
        'serviceData': 'order-4172',  # your order id
    },
    timeout=10,
)

result = response.json()

if result['result'] != 'success':
    raise RuntimeError(f"API error: {result['data']}")

invoice = result['data']

# invoice['id']  — invoice id, store it with the order
# invoice['url'] — payment page for the customer
```

Response:

```json
{
  "result": "success",
  "data": {
    "id": "ade9550d-3dc7-4fd3-b94e-3b4c12aaaa0c",
    "uid": "MXNj4m8HhcM4",
    "createDatetime": "2026-09-14 10:12:03",
    "timeToPayDatetime": "2026-09-14 11:12:03",
    "commissionFiatUSD": 0.5,
    "amountFiatUSD": 49.9,
    "url": "https://dash.bitsby.app/invoices/pay/MXNj4m8HhcM4"
  }
}
```

Store `data.id` with the order and send the customer to `data.url`—the payment page. Deliver the link any way you like: a redirect, an email, a bot message. The invoice is valid until `timeToPayDatetime` (UTC).

## Handling the notification

When an invoice moves to Paid, the service sends a POST request to the project's Webhook URL. The body is JSON; the signature is in the headers:

| Header | Value |
| --- | --- |
| `X-Timestamp` | Send time, unix time in seconds |
| `X-Signature` | `sha256=` + hex HMAC-SHA256 of the string `<timestamp>.<request body>` |

The signing key is the webhook secret. The signature is computed over the raw request body, so verify it before parsing the JSON.

**PHP**

```php showLineNumbers
<?php
$secret = 'k7QwR2mZ9tXbN4vL8sJpH3dF6yA1cE0u';

$body      = file_get_contents('php://input');
$timestamp = $_SERVER['HTTP_X_TIMESTAMP'] ?? '';
$signature = $_SERVER['HTTP_X_SIGNATURE'] ?? '';

// Reject replayed requests: allow up to 5 minutes of clock drift
if (abs(time() - (int)$timestamp) > 300) {
    http_response_code(400);
    exit;
}

$expected = 'sha256='.hash_hmac('sha256', $timestamp.'.'.$body, $secret);

if (!hash_equals($expected, $signature)) {
    http_response_code(403);
    exit;
}

$invoice = json_decode($body, true)['invoice'];

if ($invoice['status'] === 'paid') {
    // $invoice['serviceData'] — the order id passed at creation: 'order-4172'
    // $invoice['amountFiat']  — the original invoice amount: 49.9
    // Issue the order here, see the next section
}

http_response_code(200);
```

**TypeScript**

```typescript showLineNumbers
import { createHmac, timingSafeEqual } from 'node:crypto';
import express, { type Request, type Response } from 'express';

const SECRET = 'k7QwR2mZ9tXbN4vL8sJpH3dF6yA1cE0u';
const app = express();

// express.raw: the signature is computed over the raw request body
app.post('/webhook', express.raw({ type: 'application/json' }), (req: Request, res: Response) => {
    const timestamp = req.get('X-Timestamp') ?? '';
    const signature = req.get('X-Signature') ?? '';
    const body = (req.body as Buffer).toString('utf8');

    // Reject replayed requests: allow up to 5 minutes of clock drift
    if (Math.abs(Date.now() / 1000 - Number(timestamp)) > 300) {
        return res.sendStatus(400);
    }

    const expected = 'sha256=' + createHmac('sha256', SECRET)
        .update(`${timestamp}.${body}`, 'utf8')
        .digest('hex');

    const a = Buffer.from(expected);
    const b = Buffer.from(signature);

    if (a.length !== b.length || !timingSafeEqual(a, b)) {
        return res.sendStatus(403);
    }

    const { invoice } = JSON.parse(body);

    if (invoice.status === 'paid') {
        // invoice.serviceData — the order id passed at creation: 'order-4172'
        // invoice.amountFiat  — the original invoice amount: 49.9
        // Issue the order here, see the next section
    }

    res.sendStatus(200);
});

app.listen(8080);
```

**JavaScript**

```js showLineNumbers
import { createHmac, timingSafeEqual } from 'node:crypto';
import express from 'express';

const SECRET = 'k7QwR2mZ9tXbN4vL8sJpH3dF6yA1cE0u';
const app = express();

// express.raw: the signature is computed over the raw request body
app.post('/webhook', express.raw({ type: 'application/json' }), (req, res) => {
    const timestamp = req.get('X-Timestamp') ?? '';
    const signature = req.get('X-Signature') ?? '';
    const body = req.body.toString('utf8');

    // Reject replayed requests: allow up to 5 minutes of clock drift
    if (Math.abs(Date.now() / 1000 - Number(timestamp)) > 300) {
        return res.sendStatus(400);
    }

    const expected = 'sha256=' + createHmac('sha256', SECRET)
        .update(`${timestamp}.${body}`, 'utf8')
        .digest('hex');

    const a = Buffer.from(expected);
    const b = Buffer.from(signature);

    if (a.length !== b.length || !timingSafeEqual(a, b)) {
        return res.sendStatus(403);
    }

    const { invoice } = JSON.parse(body);

    if (invoice.status === 'paid') {
        // invoice.serviceData — the order id passed at creation: 'order-4172'
        // invoice.amountFiat  — the original invoice amount: 49.9
        // Issue the order here, see the next section
    }

    res.sendStatus(200);
});

app.listen(8080);
```

**Python**

```python showLineNumbers
import hashlib
import hmac
import time

from flask import Flask, request

SECRET = 'k7QwR2mZ9tXbN4vL8sJpH3dF6yA1cE0u'
app = Flask(__name__)

@app.post('/webhook')
def webhook():
    timestamp = request.headers.get('X-Timestamp', '')
    signature = request.headers.get('X-Signature', '')
    # The signature is computed over the raw request body
    body = request.get_data(as_text=True)

    # Reject replayed requests: allow up to 5 minutes of clock drift
    if abs(time.time() - int(timestamp or 0)) > 300:
        return '', 400

    expected = 'sha256=' + hmac.new(
        SECRET.encode(),
        f'{timestamp}.{body}'.encode(),
        hashlib.sha256,
    ).hexdigest()

    if not hmac.compare_digest(expected, signature):
        return '', 403

    invoice = request.get_json()['invoice']

    if invoice['status'] == 'paid':
        # invoice['serviceData'] — the order id passed at creation: 'order-4172'
        # invoice['amountFiat']  — the original invoice amount: 49.9
        # Issue the order here, see the next section
        pass

    return '', 200
```

Respond with a 2xx code within 10 seconds. Any other code, a redirect, or a timeout counts as a failed delivery: the service retries at increasing intervals from 5 minutes up to 24 hours, then stops. Offload long processing to a queue: respond with 200 first, then work on the order.

The full notification format and field reference are in the [Webhook URL](./webhook-url/index.md) section.

## Order fulfillment

A verified notification with status `paid` confirms the payment. Fulfillment steps:

1. **Find the order** by `invoice.serviceData`—the value passed at invoice creation (`order-4172`).
2. **Check by `invoice.id` whether this invoice has already been fulfilled.** A notification with the same `invoice.id` can arrive more than once—fulfill the order once and store a processed flag.
3. **Verify the amount and currency** against `invoice.amountFiat` and `invoice.currencyFiat`—these are the original invoice values and never change. `amountFiatUSD` is overwritten with the amount actually received. Compare amounts as numbers, not strings: trailing zeros are dropped, so `49.90` arrives as `49.9`. If the values don't match the order, route the invoice to manual review instead of fulfillment—such cases are covered in [Payment matching and amount mismatches](./payment-matching.md).
4. **Fulfill the order and mark it as processed.**

Do not check the payment deadline at fulfillment: the payment may have confirmed on-chain after `timeToPayDatetime`, and the merchant can match a payment to an invoice manually. The notification itself confirms the payment.

## What's next

- [API reference](./api/index.md)—invoice lists, cancellation, statistics, balances
- [Webhook signature verification](./webhook-url/signature-verification.md)—the signature mechanics in detail
- [Payment matching and amount mismatches](./payment-matching.md)—underpayment, overpayment, unmatched payments
- [HTML forms](./creating-invoices/html-forms/index.md)—accepting payments without the API