Shamim H.

Most payment problems don't show up in testing. They show up three weeks after launch, when a seller's payout is held, a subscriber is charged twice, or a price change quietly locks existing members out. That's the work I do. I've been building and fixing payment systems on Upwork since 2011, with more than 24,000 hours logged and a 100% Job Success Score. My first Stripe Connect marketplace went live in 2014. I work in Laravel/PHP and in TypeScript (Node, Express, Next.js, React), so I can fix the backend and the checkout in the same pass. What clients usually bring me: - Stripe Connect marketplaces: seller onboarding, KYC and restricted accounts, split payments, holds, refunds, disputes and payouts - Escrow and milestone payments, where buyer money has to stay separate from platform revenue until the work is delivered - Subscriptions and billing: trials, proration, pausing, failed-payment retries, coupons, and moving customers to new pricing without breaking what existing members already have - Picking and integrating a processor: Stripe, PayPal, Apple Pay, Google Pay, ACH, Wise, and options for high-risk or donation businesses - Webhooks and payment callbacks that never double-charge or silently drop an event - The store around it: Shopify (including GemPages landing pages built to match ad campaigns), WooCommerce and WordPress A few recent jobs: - Lead engineer on a B2B fashion-sourcing marketplace: brands send quote requests to several factories at once without seeing each other's bids, factories turn accepted quotes into milestone invoices, and buyer payments sit in escrow apart from platform revenue. Four apps, 680+ commits, no rollbacks. - Moved an online course from monthly billing to one-time section pricing with an upsell, while current members kept their access and billing untouched - Built a payment-provider callback service for a fintech company in a day, with alerts - Built a flight-tracking platform that checks a list of travellers on a schedule and alerts coordinators when a flight changes - Built mobile-first Shopify landing pages for a health brand, each matched to a specific Meta ad - Brought a B2B site back after an outage, then found months of "lost" enquiries sitting in an inbox nobody watched Also: a payment company's back office (roles, audit logs, merchant reporting) and a React Native pet-care app taken to store-ready. I contributed to Upwork's official agent plugin and test the Upwork MCP, and I run my own AI-assisted job matching and alerts on it, so I know how AI agents and Upwork's API behave in practice. How I work: I read your code and your Stripe dashboard before proposing anything, test on staging, and keep you updated in three parts: what's done, what needs your decision, and what's outside scope. I work US business hours and reply within a few hours. If your payments work in the demo but not in real life, send me what's happening and I'll tell you where I'd look first.