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$
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I will fix and build custom api integration and payment gateway
Umair Athar
About this gig
Payment integrations fail in the gaps, not on the happy path.
WHAT I DO
- REST and GraphQL APIs with Swagger/OpenAPI documentation
- Payment gateways: Stripe, PayPal, JazzCash, EasyPaisa, crypto
- Webhook pipelines with idempotency, retries and reconciliation
- Authentication systems: JWT, OAuth, role-based access
- Rescuing integrations that half-work and nobody understands
COMMON CHALLENGES SOLVED
- Webhook fires twice: deduplicated by event id before it reaches your ledger
- Timeout mid-charge: idempotency key, so a retry never double-charges
- Webhook never arrives: scheduled reconciliation against their records
- Refund never syncs: status read from the provider, not from a click
- Provider outage: queue, retry and alert, not a silently failed order
PRODUCTION EXPERIENCE
- CPCS: deposits and withdrawals across gateways including Bitcoin Lightning and CashApp, with encrypted keys and a full audit log.
- FleetReact: Indeed API, Plaid payments and Google Maps tracking in one platform.
- ImadNext: Easypaisa, JazzCash, Raast and PayPak alongside international cards.
Every API ships documented. An undocumented API is technical debt from launch day.
Get to know Umair Athar
Umair Athar
AI and full stack engineer building production software
- FromPakistan
- Member sinceMay 2024
- Avg. response time1 hour
Languages
Urdu, English, Hindi
I'm Umair, a full-stack and AI engineer with 5+ years shipping production software, not prototypes.
What I do:
1. AI products: RAG systems, AI agents, document processing, and chatbots grounded in your data so they don't invent answers.
2. Full-stack builds: SaaS platforms, dashboards, CRM/ERP, eCommerce, and the APIs behind them.
Recent: a multi-tenant SOC 2 compliance platform with RAG search, an AI property-report engine on live UK government data, and a store running 6 payment gateways.
Stack: Next.js, React, Node, TypeScript, MongoDB, OpenAI, Gemini, AWS.
My Portfolio
Other Software Development Services I Offer
FAQ
Which payment gateways can you integrate?
Stripe and PayPal for international, JazzCash and EasyPaisa for Pakistan, plus crypto and alternative processors. I've shipped OpenNode Bitcoin Lightning and CashApp flows in production. If your gateway has an API, I can almost certainly integrate it.
Can you work with a badly documented or legacy API?
Usually yes. A lot of this work involves thin or outdated documentation. I start with a short discovery phase to probe the system's real behaviour before quoting the full build, so surprises surface early.
REST or GraphQL?
REST is the right default for most products: simpler to cache, document and debug. GraphQL earns its complexity when many different clients need flexible queries over the same data. I'll recommend based on your actual consumers, not on trend.
What happens when the third-party API goes down?
The integration queues, retries and degrades gracefully, so a provider outage is a logged event in your system rather than a crisis in your business. That's designed in, not added after the first incident.
Do you test against live payments?
Sandbox first, then live with small real transactions before handover. Testing against both environments is part of every delivery.
What if something breaks after delivery?
If a bug in what I built turns up after delivery, I fix it. That is not an upsell. If the provider changed their API or your traffic outgrew the original design, that is new work and I will say so plainly rather than quietly bill it as a bug fix.
What happens when the provider changes their API?
Where a provider supports versioning, the integration is pinned to a version, so a change on their side cannot break you overnight. They give notice before retiring a version, and I document exactly where that version is set so the migration is a small, known job.
How does my team debug a failed payment later?
Every request and webhook is logged with a correlation id your team can search, so a customer question becomes a lookup rather than an investigation. The handover walkthrough covers where those logs live and what a healthy transaction looks like.
Do API keys or credentials need maintaining?
Rotate the keys you shared with me once the work is delivered, which takes a minute in the provider dashboard. Beyond that, keys live in environment config rather than the code, so rotating them later never requires a developer or a redeploy.
