> ## Documentation Index
> Fetch the complete documentation index at: https://next-developers.opencard.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Receipt Provider Integration

> Integration guide for receipt providers — collect receipts from merchants and POS, deliver to OpenCard, and enrich EMS transactions with VAT and line items.

Receipt providers are actors that **collect digital receipts** — from merchants, POS systems, e-commerce platforms, or your own network — and **deliver them to OpenCard**.

OpenCard attaches the receipt to the matching card transaction, extracts VAT and line items, and forwards everything to EMS apps via webhooks.

***

## The flow

```mermaid theme={null}
sequenceDiagram
    participant RP as Receipt Provider
    participant OC as OpenCard
    participant EMS as EMS

    Note over RP: You collect receipts from merchants
    OC->>RP: Match request (transaction data)
    RP->>RP: Find receipt in your collection
    RP->>OC: POST callback with receipt data
    OC->>EMS: receipt.fetched
    OC->>EMS: transaction.true.vat
    OC->>EMS: transaction.line.items
```

Your job ends at the callback to OpenCard. You never talk to EMS apps directly.

***

## What you implement

1. **Collect receipts** in your merchant network
2. **Receive match requests** from OpenCard when a transaction is receiptable
3. **POST the receipt** back to OpenCard when you have a match

→ [How it works](/receipt-providers/how-it-works) · [Callback delivery](/receipt-providers/callback-delivery) · [Payload formats](/receipt-providers/payload-formats)

***

## Auth

Callbacks to OpenCard are authenticated with **HMAC-SHA256**:

```
X-Data-Signature: HMAC-SHA256(raw_request_body, shared_client_secret)
```

You receive the shared secret from OpenCard during onboarding.

***

## Events

| `X-Event` header          | Meaning                              |
| ------------------------- | ------------------------------------ |
| `CallbackRequestResolved` | Receipt found — send receipt payload |
| `CallbackRequestDeleted`  | No match / expired — send empty body |

Contact **[support@opencard.io](mailto:support@opencard.io)** to become a receipt provider partner.