Payment Infrastructure & PSP Integrations

# Payment integrations that handle retries and failures.

Connect a PSP or repair a payment flow that gets stuck, processes a callback twice or loses track of the provider status. The work covers provider APIs, webhook handling, internal state changes and reconciliation.

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## Two deliveries. One state change.

The first event applies the payment transition. The repeated event meets the same durable key and makes no second state change.

## Example scope & report

See the project brief, proposed solution and acceptance checks for work around a public product.

[Read Stripe payment recovery: example scope ↗](/examples/payment-reliability)Public-product reference · proposed delivery plan.

## When this is useful

Fintech and SaaS teams adding a payment provider or fixing a checkout, deposit or payout integration.

- A repeated callback applies the same payment change twice.

- The provider has accepted a request, but a timeout leaves the application unsure what happened.

- Support cannot explain why a transaction is pending or how to resolve it safely.

## How the work happens

- Agree the provider contractReview authentication, signatures, API responses and status transitions. Identify the source of truth for each decision, including how to resolve an unknown outcome.

- Implement calls and callbacksUse stable operation identifiers, durable duplicate checks, bounded timeouts and controlled retries. Record enough information to link the customer request, provider attempt and internal result.

- Exercise the failure pathsTest declines, lost responses, duplicate callbacks and events arriving out of order. Document reconciliation and recovery. Record sandbox checks separately from production acceptance.

## What your team receives

- The agreed provider integration or payment-flow fix, with tests.

- A status and recovery guide for engineering and support.

- Configuration, reconciliation checks and release instructions.

## Does a successful API response mean a payment is complete?

Not always. An accepted request, an authorised payment, settlement and internal crediting can be different states. The implementation follows the provider contract and records which evidence completes each transition.

Start with a clear scope

One scoped integration or workflow from $1,500

[Book a free 30-minute discovery call ↗](/contact)One provider or workflow is agreed in the proposal. Provider onboarding, compliance decisions, production credentials and transaction fees remain client responsibilities.

Confidentiality, access, milestones and acceptance criteria are agreed before work starts. Please leave secrets out of your first enquiry.

## Related engineering services

[Backend & API Development ↗](/services/backend-api-development)[Technical Architecture & Code Audits ↗](/services/technical-architecture-code-audits)[Fintech & SaaS Engineering ↗](/services/fintech-saas-engineering)[Technical Consultation & Advisory ↗](/services/it-consulting)[AI Integration & Automation ↗](/services/ai-integration-automation)[Cybersecurity Review & Vulnerability Research ↗](/services/cybersecurity-review)[Expert Code & Architecture Review ↗](/services/code-architecture-review)

Contact: [hello@upserto.com](mailto:hello@upserto.com)