> ## Documentation Index
> Fetch the complete documentation index at: https://developer.fexpayments.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Reverse QR Flow (Counter Scan)

> Counter scan flow where the POS scans the customer wallet QR.

The POS terminal scans the **customer's** QR code. The customer receives a push notification in their wallet app and taps to approve.

<Frame>
  <img src="https://mintcdn.com/fexpayments-0eb1bb58/ePXtypRp_xROwgxZ/images/image-3.png?fit=max&auto=format&n=ePXtypRp_xROwgxZ&q=85&s=313b247f60f9c10a0570c6ef82d0bcae" alt="Image" width="906" height="527" data-path="images/image-3.png" />
</Frame>

### Prerequisites — Register a Counter (POS Terminal)

Each physical terminal should be registered once. This enables per-terminal reporting and ties scan-payment transactions to a specific terminal.

**`POST /merchant/api/v1/counters`**

```json theme={null}
{
  "name": "Till 1",
  "location": "Main entrance"
}
```

**Response:**

```json theme={null}
{
  "success": true,
  "counter": {
    "id": "ctr_xxxx",
    "merchant_id": "a1b2c3d4-...",
    "name": "Till 1",
    "location": "Main entrance",
    "status": "active",
    "webhook_secret": "whsec_xxxxxxxx"
  }
}
```

> **Save `webhook_secret`** — you will use it to verify incoming webhooks for this terminal. Treat it like a password.

### Initiate a Scan Payment

**`POST /merchant/api/v1/scan-payment`**

```json theme={null}
{
  "scan_token":    "{value decoded from customer's wallet QR}",
  "counter_id":   "ctr_xxxx",
  "amount":       49.50,
  "currency":     "USD",
  "description":  "Lunch combo",
  "expires_in":   120,
  "reference":    "ORDER-2087",
  "callback_url": "https://your-backend.example.com/webhooks/fex"
}
```

**Request fields:**

| Field          | Type    | Required | Description                                     |
| -------------- | ------- | :------: | ----------------------------------------------- |
| `scan_token`   | string  |     ✅    | Value decoded from the customer's wallet QR     |
| `counter_id`   | string  |     ✅    | ID of the scanning terminal                     |
| `amount`       | float   |     ✅    | Charge amount                                   |
| `currency`     | string  |     —    | Default: `USD`                                  |
| `expires_in`   | integer |     —    | Seconds for customer to approve. Default: `300` |
| `description`  | string  |     —    | Shown to customer in push notification          |
| `reference`    | string  |     —    | Your internal order or invoice ID               |
| `callback_url` | string  |     —    | URL to receive the `payment.completed` webhook  |

**Response `201 Created`:**

```json theme={null}
{
  "success": true,
  "payment_intent": {
    "id": "pi_yyyy",
    "status": "pending_approval",
    "amount": 49.50,
    "expires_at": "2025-01-01T12:37:00Z"
  }
}
```

The customer receives a push notification immediately. Their approval fires a `payment.completed` webhook to your `callback_url`.