Source 88fa7b4d873dc3b766dc5dd6

---
name: sumup
description: Implement SumUp checkout flows end-to-end. Use when writing or reviewing SumUp Checkouts API calls, Card Widget mounts, Hosted Checkout setup, recurring tokenization, Terminal SDK / Cloud API reader checkouts, or 3DS / webhook handling.
license: Apache-2.0
---

# SumUp Checkout Integrations

Knowledge and APIs can change. Always prefer the latest SumUp docs in markdown format over stale memory.

- Docs root: `https://developer.sumup.com/`
- LLM entrypoint: `https://developer.sumup.com/llms.txt`
- Markdown page format example: `https://developer.sumup.com/terminal-payments/cloud-api/index.md`

Use this skill to implement end-to-end SumUp checkouts for:

- Terminal payments (native mobile SDKs, Cloud API for Solo, or Payment Switch)
- Online payments (Card Widget and API-orchestrated checkout flow)

## Related Skills

- `sumup-best-practices` for integration-path and security decisions.
- `upgrade-sumup` for SDK/API version upgrades and migrations.
- `sumup-debug` for troubleshooting failing integrations.
- `sumup-mcp` for configuring and using `https://mcp.sumup.com/mcp`.
- `sumup-testing` for sandbox setup and end-to-end QA.

## Quick Decision Tree

```text
Need to accept a payment?
├─ In-person (card-present) → terminal
│  ├─ Native mobile app + direct reader flow → terminal/mobile (iOS SDK or Android Reader SDK)
│  ├─ Non-native POS/backend controls Solo reader → terminal/platform-agnostic (Cloud API)
│  └─ Legacy app handoff to SumUp app explicitly required → terminal/legacy-lightweight (Payment Switch)
└─ Online (card-not-present) → online
   ├─ Fastest, no embed needed, redirect OK → online/no-code (Hosted Checkout)
   ├─ Embedded UI, no PCI burden → online/low-complexity (Card Widget)
   ├─ Mobile app (iOS native | React Native) → online/mobile (Swift / React Native SDK)
   ├─ Save card / subscriptions → online/recurring (Customers + tokenization)
   └─ Custom orchestration → online/custom (Checkouts API + 3DS + webhooks)
```

## Start Here

1. Classify the requested flow:
   - `terminal`: in-person card-present payment
   - `online`: e-commerce/web/app card-not-present payment
   - `hybrid`: both (for example, web checkout + in-store Solo)
2. Pick integration path:
   - `terminal/mobile`: iOS SDK or Android Reader SDK
   - `terminal/platform-agnostic`: Cloud API with Solo readers
   - `terminal/legacy-lightweight`: Payment Switch
   - `online/no-code`: Hosted Checkout
   - `online/low-complexity`: Card Widget
   - `online/mobile`: Swift Checkout SDK or React Native SDK
   - `online/recurring`: Customers + tokenization + recurring charges
   - `online/custom`: Checkouts API + 3DS + webhooks
3. Confirm credentials and environment:
   - API key or OAuth access token
   - Affiliate Key for card-present flows
   - Merchant code and currency alignment
   - Sandbox merchant account for non-production testing
4. Ask for missing critical inputs before implementation:
   - integration channel (mobile SDK, Cloud API, Card Widget, or API-orchestrated)
   - target market/currency and merchant code
   - auth model (API key vs OAuth)
   - webhook endpoint and idempotency strategy
   - existing constraints (legacy compatibility, migration, PCI scope)
5. Apply the implementation pattern from `references/checkout-playbook.md`.
6. Use `references/README.md` and open only the single most relevant entrypoint for the request.

## Non-Negotiable Rules

- Keep secret API keys and OAuth client secrets server-side only.
- Never handle raw PAN/card data directly.
- Create online checkouts server-to-server.
- Prefer Card Widget and SDK-provided checkout experiences to avoid handling raw card details.
- For card-present integrations, include the Affiliate Key and ensure app identifiers match the key setup.
- Avoid Payment Switch unless the user explicitly requests it or has a hard legacy constraint.
- Use unique transaction references (`checkout_reference`, `foreignTransactionId`, or equivalent) to prevent duplicates and improve reconciliation.
- Do not use endpoints marked as deprecated.
- Prefer endpoints that accept `merchant_code` as an explicit parameter when equivalent alternatives exist.
- Treat webhook events as notifications only; verify state through API reads.
- After a widget/client callback reports success, always verify final checkout state on the backend before confirming order/payment success.

## Implementation Workflow

1. Set up auth and merchant context.
2. Create checkout request with unique reference and correct currency.
3. Complete checkout via chosen channel:
   - terminal SDK checkout call
   - Cloud API reader checkout
   - Card Widget
   - direct checkout processing flow
4. Handle async outcomes:
   - SDK callback / activity result / event stream
   - 3DS `next_step` redirect flow
   - webhook delivery + API verification
5. Return normalized result (status, transaction identifiers, retry guidance).

## Required Response Contract

Every solution should state:

1. Chosen integration path and why.
2. End-to-end sequence (server, client, webhook/async verification).
3. Exact endpoint set, confirming no deprecated endpoints and preference for `merchant_code`-accepting endpoints.
4. Failure and retry handling (timeouts, duplicate refs, webhook retries).
5. Test plan for success, deliberate failure, and reconciliation checks.

## Validation Checklist

- Test and capture both successful payment and deliberate failure case (`amount = 11` in test mode).
- Verify behavior for duplicate transaction references.
- Verify timeout/session expiry behavior in the selected checkout path.
- Verify webhook retries and idempotent processing.
- Verify reconciliation fields are stored (checkout id, transaction id/code, merchant code, reference).

## References

- Use `references/README.md` to pick the right reference file.
- Each reference file includes its own canonical markdown docs URL. Prefer that URL over stale memory.
- Open `references/hosted-checkout/README.md`, `references/recurring-tokenization/README.md`, or `references/security/README.md` directly when the request maps to those flows.