> ## 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 Callback API

> Reference for the inbound receipt provider callback API — POST matched receipt payloads to OpenCard with HMAC-SHA256 signatures on api.opencard.io.

Receipt providers POST enriched receipt data to OpenCard when a match is found.

<Info>
  This is the **inbound** callback API. For the full delivery flow (headers, HMAC, payloads) see [Callback delivery](/receipt-providers/callback-delivery).
</Info>

## Base URL

```
https://api.opencard.io/api
```

Sandbox: `https://sandbox-api.opencard.io/api`

## Auth

`X-Data-Signature` header — HMAC-SHA256 of the raw request body with your client secret.

## Key endpoint

| Method | Path                                        | Purpose                      |
| ------ | ------------------------------------------- | ---------------------------- |
| `POST` | `/v1/service/marcet/callback/{referenceId}` | Deliver matched receipt data |