# Apple IAP Protocol (Frontend <-> Backend)

This document defines the Apple In-App Purchase verification and grant contract for Eryao Flutter app.

Protocol verification status:

- Backend route source: `backend/src/v1/payments/router.py`
- Backend service source: `backend/src/v1/payments/service.py`
- Backend verifier source: `backend/src/v1/payments/apple_verifier.py`
- Backend schema source: `backend/src/v1/payments/schemas.py`
- Current status: aligned

## Compatibility strategy

- Current strategy: additive evolution (`backward-compatible`).
- Breaking change requires explicit migration + rollback notes (`requires-migration`).

## Route overview

- Verify transaction: `POST /api/v1/payments/apple/transactions/verify`
- Apple server notification: `POST /api/v1/payments/apple/notifications` (server-to-server)

## Verify transaction

### `POST /api/v1/payments/apple/transactions/verify`

Verify and grant credits for an Apple IAP transaction.

**Authorization**: Requires authenticated session. User identity from JWT `sub`.

**Request:**

```json
{
  "productCode": "new_user_pack",
  "appStoreProductId": "com.meeyao.qianwen.new_user_pack",
  "transactionId": "2000000123456789",
  "signedTransactionInfo": "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsIng1YyI6WyJNSUlFTURDQ0E3YWdBd0lCQWdJUWFQeF...",
  "appAccountToken": "uuid-or-null"
}
```

**Fields:**
- `productCode` (required): string, max 32 chars, product code from packages API
- `appStoreProductId` (required): string, max 128 chars, Apple product ID
- `transactionId` (required): string, max 64 chars, Apple transaction ID
- `signedTransactionInfo` (required): string, JWS signed transaction info from Apple
- `appAccountToken` (optional): UUID, app account token for user association

**Response (200):**

```json
{
  "status": "granted",
  "productCode": "new_user_pack",
  "transactionId": "2000000123456789",
  "creditsAdded": 60,
  "newBalance": 160,
  "ledgerEventId": "payment.apple_iap:2000000123456789"
}
```

**Status values:**
- `granted`: Transaction verified and credits added
- `already_granted`: Transaction already processed for this user

**Error codes:**

| code | status | meaning |
|---|---:|---|
| `PAYMENT_PRODUCT_NOT_FOUND` | 404 | `productCode` does not exist or is not enabled |
| `PAYMENT_PRODUCT_MISMATCH` | 422 | Client product ID does not match backend/Apple verification result |
| `PAYMENT_ENVIRONMENT_MISMATCH` | 422 | Transaction environment (Sandbox/Production) does not match server environment |
| `PAYMENT_TRANSACTION_INVALID` | 422 | Apple signed transaction invalid, signature verification failed, or payload malformed |
| `PAYMENT_TRANSACTION_REVOKED` | 409 | Transaction has been revoked or refunded, grant not allowed |
| `PAYMENT_TRANSACTION_CONFLICT` | 409 | Transaction already processed by another user or in conflicting state |
| `PAYMENT_STARTER_PACK_INELIGIBLE` | 409 | Current email identity has already purchased starter pack |

## Apple server notification

### `POST /api/v1/payments/apple/notifications`

Server-to-server notification from Apple for refund/revoke events.

**Authorization**: None (Apple server origin).

**Request:**

```json
{
  "signedPayload": "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsIng1YyI6WyJNSUlFTURDQ0E3YWdBd0lCQWdJUWFQeF..."
}
```

**Response (200):** Empty success response.

**Behavior:**
- Parses notification type and transaction info
- For `REFUND`, `REVOKE`, `DID_FAIL_TO_RENEW` notifications, processes refund clawback
- Refund reduces user balance by original purchase amount (or remaining balance if insufficient)

## Product mapping

Products are configured in `backend/src/core/config/static/packages/mapping.yaml`:

```yaml
product_mappings:
  new_user_pack:
    app_store_product_id: com.meeyao.qianwen.new_user_pack
    credits: 60
    type: starter
    sort_order: 0
    enabled: true
```

## Starter pack eligibility

- Starter pack (`type: starter`) can only be purchased once per email identity
- Backend tracks purchase via `register_bonus_claims.has_purchased_starter_pack`
- If already purchased, returns `PAYMENT_STARTER_PACK_INELIGIBLE` (409)

## Ledger integration

- Successful purchases create a ledger entry with:
  - `change_type: purchase`
  - `biz_type: payment`
  - `biz_id: apple_iap_transactions.id`
  - `metadata.ext` containing Apple IAP details

- Refunds create a ledger entry with:
  - `change_type: refund`
  - `biz_type: payment`
  - `metadata.ext.original_event_id` referencing original purchase event

## Error contract linkage

- All errors use RFC7807 with extension `code` and optional `params`.
- Error code registry source: `docs/protocols/common/http-error-codes.md`.