sub2api/docs/PAYMENT.md

# Payment System Configuration Guide

Sub2API has a built-in payment system that enables user self-service top-up without deploying a separate payment service.

---

## Table of Contents

- [Supported Payment Methods](#supported-payment-methods)
- [Quick Start](#quick-start)
- [System Settings](#system-settings)
- [Provider Configuration](#provider-configuration)
- [Provider Instance Management](#provider-instance-management)
- [Webhook Configuration](#webhook-configuration)
- [Payment Flow](#payment-flow)
- [Migrating from Sub2ApiPay](#migrating-from-sub2apipay)

---

## Supported Payment Methods

| Provider | Payment Methods | Description |
|----------|----------------|-------------|
| **EasyPay** | Alipay, WeChat Pay | Third-party aggregation via EasyPay protocol |
| **Alipay (Direct)** | PC Page Pay, H5 Mobile Pay | Direct integration with Alipay Open Platform, auto-switches by device |
| **WeChat Pay (Direct)** | Native QR Code, H5 Pay | Direct integration with WeChat Pay APIv3, mobile-first H5 |
| **Stripe** | Card, Alipay, WeChat Pay, Link, etc. | International payments, multi-currency support |

> Alipay/WeChat Pay direct and EasyPay can coexist. Direct channels connect to payment APIs directly with lower fees; EasyPay aggregates through third-party platforms with easier setup.

> **EasyPay Recommendation**: [ZPay](https://z-pay.cn/?uid=23808) (`https://z-pay.cn/?uid=23808`) is recommended as an EasyPay provider (link contains the referral code of [Sub2ApiPay](https://github.com/touwaeriol/sub2apipay) original author [@touwaeriol](https://github.com/touwaeriol) — feel free to remove it). ZPay supports **individual users** (no business license required) with up to 10,000 CNY daily transactions; business-licensed accounts have no limit. Please evaluate the security, reliability, and compliance of any third-party payment provider on your own — this project does not endorse or guarantee any of them.

---

## Quick Start

1. Go to Admin Dashboard → **Settings** → **Payment Settings** tab
2. Enable **Payment**
3. Configure basic parameters (amount range, timeout, etc.)
4. Add at least one provider instance in **Provider Management**
5. Users can now top up from the frontend

---

## System Settings

Configure the following in Admin Dashboard **Settings → Payment Settings**:

### Basic Settings

| Setting | Description | Default |
|---------|-------------|---------|
| **Enable Payment** | Enable or disable the payment system | Off |
| **Product Name Prefix** | Prefix shown on payment page | - |
| **Product Name Suffix** | Suffix (e.g., "Credits") | - |
| **Minimum Amount** | Minimum single top-up amount | 1 |
| **Maximum Amount** | Maximum single top-up amount (empty = unlimited) | - |
| **Daily Limit** | Per-user daily cumulative limit (empty = unlimited) | - |
| **Order Timeout** | Order timeout in minutes (minimum 1) | 5 |
| **Max Pending Orders** | Maximum concurrent pending orders per user | 3 |
| **Load Balance Strategy** | Strategy for selecting provider instances | Least Amount |

### Load Balance Strategies

| Strategy | Description |
|----------|-------------|
| **Round Robin** | Distribute orders to instances in rotation |
| **Least Amount** | Prefer instances with the lowest daily cumulative amount |

### Cancel Rate Limiting

Prevents users from repeatedly creating and canceling orders:

| Setting | Description |
|---------|-------------|
| **Enable Limit** | Toggle |
| **Window Mode** | Sliding / Fixed window |
| **Time Window** | Window duration |
| **Window Unit** | Minutes / Hours |
| **Max Cancels** | Maximum cancellations allowed within the window |

### Help Information

| Setting | Description |
|---------|-------------|
| **Help Image** | Customer service QR code or help image (supports upload) |
| **Help Text** | Instructions displayed on the payment page |

---

## Provider Configuration

Each provider type requires different credentials. Select the type when adding a new provider instance in **Provider Management → Add Provider**.

> **Callback URLs are auto-generated**: When adding a provider, the Notify URL and Return URL are automatically constructed from your site domain. You only need to confirm the domain is correct.

### EasyPay

Compatible with any payment service that implements the EasyPay protocol.

| Parameter | Description | Required |
|-----------|-------------|----------|
| **Merchant ID (PID)** | EasyPay merchant ID | Yes |
| **Merchant Key (PKey)** | EasyPay merchant secret key | Yes |
| **API Base URL** | EasyPay API base address | Yes |
| **Alipay Channel ID** | Specify Alipay channel (optional) | No |
| **WeChat Channel ID** | Specify WeChat channel (optional) | No |

### Alipay (Direct)

Direct integration with Alipay Open Platform. Supports PC page pay and H5 mobile pay.

| Parameter | Description | Required |
|-----------|-------------|----------|
| **AppID** | Alipay application AppID | Yes |
| **Private Key** | RSA2 application private key | Yes |
| **Alipay Public Key** | Alipay public key | Yes |

### WeChat Pay (Direct)

Direct integration with WeChat Pay APIv3. Supports Native QR code and H5 payment.

| Parameter | Description | Required |
|-----------|-------------|----------|
| **AppID** | WeChat Pay AppID | Yes |
| **Merchant ID (MchID)** | WeChat Pay merchant ID | Yes |
| **Merchant API Private Key** | Merchant API private key (PEM format) | Yes |
| **APIv3 Key** | 32-byte APIv3 key | Yes |
| **WeChat Pay Public Key** | WeChat Pay public key (PEM format) | Yes |
| **WeChat Pay Public Key ID** | WeChat Pay public key ID | No |
| **Certificate Serial Number** | Merchant certificate serial number | No |

### Stripe

International payment platform supporting multiple payment methods and currencies.

| Parameter | Description | Required |
|-----------|-------------|----------|
| **Secret Key** | Stripe secret key (`sk_live_...` or `sk_test_...`) | Yes |
| **Publishable Key** | Stripe publishable key (`pk_live_...` or `pk_test_...`) | Yes |
| **Webhook Secret** | Stripe Webhook signing secret (`whsec_...`) | Yes |

---

## Provider Instance Management

You can create **multiple instances** of the same provider type for load balancing and risk control:

- **Multi-instance load balancing** — Distribute orders via round-robin or least-amount strategy
- **Independent limits** — Each instance can have its own min/max amount and daily limit
- **Independent toggle** — Enable/disable individual instances without affecting others
- **Refund control** — Enable or disable refunds per instance
- **Payment methods** — Each instance can support a subset of payment methods
- **Ordering** — Drag to reorder instances

### Instance Limit Configuration

Each instance supports these limits:

| Limit | Description |
|-------|-------------|
| **Minimum Amount** | Minimum order amount accepted by this instance |
| **Maximum Amount** | Maximum order amount accepted by this instance |
| **Daily Limit** | Daily cumulative transaction limit for this instance |

> During load balancing, instances that exceed their limits are automatically skipped.

---

## Webhook Configuration

Payment callbacks are essential for the payment system to work correctly.

### Callback URL Format

When adding a provider, the system auto-generates callback URLs from your site domain:

| Provider | Callback Path |
|----------|-------------|
| **EasyPay** | `https://your-domain.com/api/v1/payment/webhook/easypay` |
| **Alipay (Direct)** | `https://your-domain.com/api/v1/payment/webhook/alipay` |
| **WeChat Pay (Direct)** | `https://your-domain.com/api/v1/payment/webhook/wxpay` |
| **Stripe** | `https://your-domain.com/api/v1/payment/webhook/stripe` |

> Replace `your-domain.com` with your actual domain. For EasyPay / Alipay / WeChat Pay, the callback URL is auto-filled when adding the provider — no manual configuration needed.

### Stripe Webhook Setup

1. Log in to [Stripe Dashboard](https://dashboard.stripe.com/)
2. Go to **Developers → Webhooks**
3. Add an endpoint with the callback URL
4. Subscribe to events: `payment_intent.succeeded`, `payment_intent.payment_failed`
5. Copy the generated Webhook Secret (`whsec_...`) to your provider configuration

### Important Notes

- Callback URLs must use **HTTPS** (required by Stripe, strongly recommended for others)
- Ensure your firewall allows callback requests from payment platforms
- The system automatically verifies callback signatures to prevent forgery
- Balance top-up is processed automatically upon successful payment — no manual intervention needed

---

## Payment Flow

```
User selects amount and payment method
       │
       ▼
  Create Order (PENDING)
  ├─ Validate amount range, pending order count, daily limit
  ├─ Load balance to select provider instance
  └─ Call provider to get payment info
       │
       ▼
  User completes payment
  ├─ EasyPay     → QR code / H5 redirect
  ├─ Alipay      → PC page pay / H5 mobile pay
  ├─ WeChat Pay  → Native QR / H5 pay
  └─ Stripe      → Payment Element (card/Alipay/WeChat/etc.)
       │
       ▼
  Webhook callback verified → Order PAID
       │
       ▼
  Auto top-up to user balance → Order COMPLETED
```

### Order Status Reference

| Status | Description |
|--------|-------------|
| `PENDING` | Waiting for user to complete payment |
| `PAID` | Payment confirmed, awaiting balance credit |
| `COMPLETED` | Balance credited successfully |
| `EXPIRED` | Timed out without payment |
| `CANCELLED` | Cancelled by user |
| `FAILED` | Balance credit failed, admin can retry |
| `REFUND_REQUESTED` | Refund requested |
| `REFUNDING` | Refund in progress |
| `REFUNDED` | Refund completed |

### Timeout and Fallback

- Before marking an order as expired, the background job queries the upstream payment status first
- If the user has actually paid but the callback was delayed, the system will reconcile automatically
- The background job runs every 60 seconds to check for timed-out orders

---

## Migrating from Sub2ApiPay

If you previously used [Sub2ApiPay](https://github.com/touwaeriol/sub2apipay) as an external payment system, you can migrate to the built-in payment system:

### Key Differences

| Aspect | Sub2ApiPay | Built-in Payment |
|--------|-----------|-----------------|
| Deployment | Separate service (Next.js + PostgreSQL) | Built into Sub2API, no extra deployment |
| Payment Methods | EasyPay, Alipay, WeChat, Stripe | Same |
| Configuration | Environment variables + separate admin UI | Unified in Sub2API admin dashboard |
| Top-up Integration | Via Admin API callback | Internal processing, more reliable |
| Subscription Plans | Supported | Not yet (planned) |
| Order Management | Separate admin interface | Integrated in Sub2API admin dashboard |

### Migration Steps

1. Enable payment in Sub2API admin dashboard and configure providers (use the same payment credentials)
2. Update webhook callback URLs to Sub2API's callback endpoints
3. Verify that new orders are processed correctly via built-in payment
4. Decommission the Sub2ApiPay service

> **Note**: Historical order data from Sub2ApiPay will not be automatically migrated. Keep Sub2ApiPay running for a while to access historical records.