Sumup Best Practices

SumUp Integration Decisions and Best Practices

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

Use this skill for architecture and security decisions, not implementation walkthroughs.

Quick Decision Tree

Need to accept a payment?├─ In-person (card-present)│  ├─ Native mobile app controls reader directly -> iOS Terminal SDK / Android Reader SDK│  ├─ POS/backend controls Solo from non-native environment -> Cloud API│  └─ Legacy handoff to SumUp app is mandatory -> Payment Switch└─ Online (card-not-present)   ├─ Fastest redirect flow, no embed required -> Hosted Checkout   ├─ Embedded payment form with low PCI scope -> Card Widget   ├─ Mobile app checkout UX -> Swift Checkout SDK / React Native SDK   ├─ Save card and charge later -> Customers + tokenization   └─ Custom orchestration needs -> Checkouts API + 3DS + webhooks

Start Here

1. Classify the request: terminal, online, or hybrid.
2. Choose the lowest-complexity viable path first:
   • Prefer Hosted Checkout or Card Widget before custom orchestration.
   • Prefer Cloud API for non-native Solo control.
3. Select auth model:
   • API key for single-merchant server integrations.
   • OAuth 2.0 for delegated or multi-merchant apps.
4. Confirm restricted access and affiliate prerequisites:
   • payments scope activation where needed.
   • Affiliate Key plus app/bundle identifier alignment for card-present.
5. Confirm operational constraints:
   • Currency/merchant alignment
   • Webhook endpoint readiness and idempotency
   • Legacy compatibility requirements

Non-Negotiable Rules

• Keep API keys and OAuth secrets server-side only.
• Never handle raw PAN/card details directly.
• Create online checkouts server-to-server.
• Prefer hosted/widget/SDK checkout UI over custom card handling.
• Avoid deprecated endpoints.
• Use unique transaction references (checkout_reference, foreignTransactionId, or equivalent).
• Treat webhook callbacks as signals and verify final state via API before fulfillment.
• Assume retries and duplicate deliveries; enforce idempotent backend handling.

Required Response Contract

When giving guidance, always return:

1. Chosen integration path with a brief why.
2. Credential model recommendation (API key vs OAuth) and scope requirements.
3. Security posture checklist for the chosen path.
4. Risks/trade-offs and when to pick a different path.
5. Minimum validation plan before production rollout.

Hand-off to Implementation Skills

• Use sumup for end-to-end implementation steps.
• Use upgrade-sumup for SDK/API migrations.
• Use sumup-debug for failure diagnosis.
• Use sumup-testing for sandbox and QA setup.