---
name: ck-payment-integration
description: Integrate payments with SePay (VietQR), Polar, Stripe, Paddle, or Creem.io. Use for checkout flows, subscription management, webhook handling, QR code payments, and software licensing.
---

# Payment Integration

Production payment processing across SePay, Polar, Stripe, Paddle, and Creem.io.

## When to Use

- Setting up payment gateway checkout or processing
- Building subscription management (trials, upgrades, billing)
- Handling webhooks with idempotency
- Implementing QR code payments (VietQR/NAPAS)
- Software licensing with device activation
- Multi-provider order management

## Don't Use When

- Simple donation buttons (use Ko-fi or Buy Me a Coffee embed)
- Internal transfer tools without customer-facing payments

## Platform Selection

| Platform | Best For |
|----------|----------|
| **SePay** | Vietnamese market, VND, bank transfers, VietQR |
| **Polar** | Global SaaS, subscriptions, automated benefits |
| **Stripe** | Enterprise, Connect platforms, custom checkout |
| **Paddle** | MoR subscriptions, global tax compliance |
| **Creem.io** | MoR + licensing, revenue splits, no-code checkout |

## General Integration Flow

```
auth → products → checkout → webhooks → events
```

## Key Capabilities

| Platform | Rate Limit | Highlights |
|----------|-----------|------------|
| SePay | 2 req/s | QR/bank/cards, 44+ VN banks |
| Polar | 300 req/min | MoR, usage billing, GitHub/Discord benefits |
| Stripe | varies | CheckoutSessions, Billing, Connect, Payment Element |
| Paddle | varies | MoR overlay/inline, Retain churn prevention, tax |
| Creem.io | varies | MoR, device licensing, revenue splits |

## Security Rules

- Store all API keys in environment variables — never hardcode
- Always verify webhook signatures before processing events
- Use idempotency keys for checkout and subscription operations
- Implement proper session token handling for embedded flows

## Reference Files

- `references/sepay.md` - SePay auth, VietQR, webhooks, SDK
- `references/polar.md` - Polar products, checkouts, subscriptions, benefits
- `references/stripe.md` - Stripe best practices, SDKs, CLI, Payment Element
- `references/paddle.md` - Paddle MoR, overlay/inline checkout, subscriptions
- `references/creem.md` - Creem MoR, licensing, no-code checkout, webhooks
- `references/multi-provider.md` - Unified orders, currency conversion patterns

## External Docs

- Stripe: https://docs.stripe.com/llms.txt
- Paddle: https://developer.paddle.com/llms.txt
- Creem: https://docs.creem.io/llms.txt