Use this skill for diagnosis and remediation of failing SumUp integrations.
Fast Triage Matrix
- Classify symptom:
- Auth/signature error
- Checkout creation/processing error
- Widget/client-side mount or flow error
- Async mismatch (success in UI, failure in backend state)
- Capture evidence:
- request/response payloads (sanitized), HTTP status, error code/message
- checkout id, merchant code,
checkout_reference - webhook delivery id and signature verdict
- Reproduce in sandbox before changing production behavior.
Common Failures and Fixes
HMAC signature mismatch (x-payload-signature)
Symptoms:
- Webhook verification fails for all events or intermittently.
Likely causes:
- Body parser mutates payload before verification.
- Wrong webhook secret/environment pair.
- Digest computed with non-raw body bytes.
Fix:
- Verify against raw request body bytes.
- Ensure HMAC SHA-256 with exact configured secret.
- Confirm secret belongs to the same merchant/environment.
Verify:
- Signature validation passes for replayed payload and for live sandbox webhook.
Expired checkout/session window
Symptoms:
- Payment attempt fails after delay, stale checkout status, or timeout flow.
Likely causes:
- Checkout left pending beyond validity window.
- Frontend retries with expired checkout id.
Fix:
- Create a new checkout for each retry attempt.
- Add frontend timeout handling that requests a fresh checkout.
Verify:
- Retried flow always uses new checkout id/reference and succeeds in sandbox.
Missing scope activation or auth mismatch
Symptoms:
- 401/403 responses despite valid credentials.
Likely causes:
- Missing
paymentsor other required scope. - API key used where OAuth is required, or vice versa.
Fix:
- Confirm auth model for integration type.
- Request/enable required scopes and re-issue token/key as needed.
Verify:
- Previously failing endpoint succeeds with least-privilege valid credentials.
Currency and merchant mismatch
Symptoms:
- Checkout rejected for currency or merchant constraints.
Likely causes:
- Checkout currency not enabled for merchant.
- Wrong merchant selected in multi-merchant context.
Fix:
- Validate merchant and currency before checkout creation.
- Enforce mapping rules in backend validation layer.
Verify:
- Invalid combinations are blocked early; valid combinations process.
Affiliate key / app identifier mismatch
Symptoms:
- Card-present flows fail or cannot initialize correctly.
Likely causes:
- Bundle ID/app ID does not match affiliate key configuration.
- Missing affiliate metadata in card-present requests.
Fix:
- Align app identifiers with affiliate key setup.
- Include required affiliate data for terminal/cloud flows.
Verify:
- Device/reader checkout path initializes and completes in sandbox/test device.
Duplicate checkout_reference
Symptoms:
- Duplicate or conflicting checkout outcomes, reconciliation confusion.
Likely causes:
- Non-unique reference generation.
- Retry logic reuses stale reference without idempotency safeguards.
Fix:
- Generate unique deterministic references per logical payment intent.
- Add duplicate detection and safe retry behavior.
Verify:
- Duplicate attempts are rejected or reconciled without double fulfillment.
Card Widget blocked or not mounting
Symptoms:
- Widget fails to render or emits
error/init failures.
Likely causes:
- Script blocked by CSP or domain policy.
- Invalid checkout id or environment mismatch.
- Frontend initialization race conditions.
Fix:
- Allow required SumUp script origin in CSP and JS origins config.
- Confirm checkout id environment and lifecycle.
- Mount only after script load and DOM ready.
Verify:
- Widget consistently mounts and can complete test payments.
Required Response Contract
For each debugging answer, include:
- Most likely root cause ranked by confidence.
- Minimal reproducible check to confirm/disprove each hypothesis.
- Exact fix steps with low-risk rollout advice.
- Post-fix verification checklist.
- Any monitoring/logging improvements to prevent recurrence.