You will get a third-party API or webhook integration built into your app
Project details
Integrations look simple until the network misbehaves. Then the same payment gets recorded twice, a webhook fires while your server is restarting, a retry creates a duplicate order, and someone in support spends a morning reconciling rows by hand.
I build the boring parts that stop this. Idempotency keys so a repeated event is recognised rather than replayed. Retry handling that fails safely instead of half-committing. Signature verification so an endpoint that is open to the internet is not open to everyone. Logging you can actually read when something does go wrong at 2am.
I have shipped this in production: Stripe Checkout and Connect with payouts and webhook handling, bank transaction sync into a live application, and serverless automation running on Cloudflare Workers.
Typical work: payment providers, CRMs, email and messaging platforms, internal APIs between your own systems, and scheduled jobs that move data on a timer.
Stack: Node.js, TypeScript, NestJS, Express, Next.js API routes, Cloudflare Workers, PostgreSQL, Prisma.
Not sure which tier fits or whether this is even the right approach? Message me first, it costs nothing.
I build the boring parts that stop this. Idempotency keys so a repeated event is recognised rather than replayed. Retry handling that fails safely instead of half-committing. Signature verification so an endpoint that is open to the internet is not open to everyone. Logging you can actually read when something does go wrong at 2am.
I have shipped this in production: Stripe Checkout and Connect with payouts and webhook handling, bank transaction sync into a live application, and serverless automation running on Cloudflare Workers.
Typical work: payment providers, CRMs, email and messaging platforms, internal APIs between your own systems, and scheduled jobs that move data on a timer.
Stack: Node.js, TypeScript, NestJS, Express, Next.js API routes, Cloudflare Workers, PostgreSQL, Prisma.
Not sure which tier fits or whether this is even the right approach? Message me first, it costs nothing.
Programming Languages
HTML & CSS, JavaScript, TypeScriptCoding Expertise
Cross Browser & Device Compatibility, Performance Optimization, W3C Markup Validation ServiceWhat's included
| Service Tiers |
Starter
$100
|
Standard
$250
|
Advanced
$500
|
|---|---|---|---|
| Delivery Time | 3 days | 5 days | 6 days |
Number of Revisions | 1 | 2 | 3 |
Design Customization | - | ||
Content Upload | - | - | |
Responsive Design | |||
Source Code |
Optional add-ons
You can add these on the next page.
Fast Delivery
+$40 - $100
Additional Revision
+$40
Each additional service or endpoint
+$100
30 days of post-launch support
+$150Frequently asked questions
About Vitaliy
Full-Stack Developer | AI SaaS, LLM Integration | React, Next.js, Node
Kyiv, Ukraine - 3:01 pm local time
I'm Vitaliy, a full-stack developer with 3+ years of commercial experience shipping web products end to end: frontend, backend, database, deployment. My focus is applications with LLMs inside them, where the AI has to be reliable enough to actually ship.
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WHAT I BUILD
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▸ SaaS platforms and internal dashboards, from empty repo to production
▸ AI features grounded in real data: assistants, chat, report generation, document processing
▸ REST APIs, authentication, role-based access, Stripe subscriptions and payouts
▸ Third-party integrations and webhook pipelines that stay correct under retries
▸ Marketing sites and landing pages built for speed and Core Web Vitals
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STACK
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▸ Frontend: React, Next.js, Astro, TypeScript, Tailwind CSS, Redux, TanStack Query, Zod
▸ Backend: Node.js, NestJS, Express, REST APIs, JWT auth, webhooks
▸ Databases: PostgreSQL, Prisma, MongoDB, Supabase, Firebase
▸ AI: Anthropic API, xAI Grok API, LLM integration and prompt design
▸ Infrastructure: Cloudflare Workers, D1, Durable Objects, Vercel, Git
▸ CMS and payments: Strapi, WordPress, Stripe (Checkout + Connect)
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SELECTED WORK
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🔹 Money Track
An AI personal finance tracker. The interesting part is the guardrail: a deterministic core owns every number in the system, and a validation step blocks any figure the model did not get from the canonical SQL layer. The advisor explains and recommends, but it cannot invent a total. Bank sync over webhooks, per-user data isolation at the infrastructure level. Built with React, TypeScript, Cloudflare Workers, Durable Objects, D1, Hono, Anthropic API. Demo account included, no signup needed.
🔹 Answerly, early-stage startup
Sole developer. Built the whole product end to end: real-time chat between users, registration and auth, Stripe payments. React, Node.js, Firebase, Stripe.
🔹 PPC io
Full multi-page marketing site in Astro, solo, maintained for over a year. Later migrated all content from Strapi to Astro content collections, which removed an external dependency and simplified the build and deploy path.
🔹 Agency client work, since 2023
Next.js applications and marketing sites for a design agency: Stripe Checkout and Connect with payouts and webhook handling, PostgreSQL, Firebase, full ownership from Figma to production.
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HOW I WORK
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I use Claude Code every day, with my own workflows for building, refactoring and review. That is a speed advantage, not a substitute for engineering: I read what it produces, test it, and own the result either way. A model instruction is never a guarantee, a check is.
I ask the awkward questions early, when they are still cheap to answer, and I send updates you can react to instead of a silent two weeks.
Available 30+ hours per week, based in Ukraine (UTC+3), with solid overlap for European and US-morning calls.
If you're building a SaaS product or adding AI to one you already have, send me a message with what you're working on.
Steps for completing your project
After purchasing the project, send requirements so Vitaliy can start the project.
Delivery time starts when Vitaliy receives requirements from you.
Vitaliy works on your project following the steps below.
Revisions may occur after the delivery date.
Map the flow
Before writing anything I confirm what triggers what, and what must be true after each step. Most integration bugs are specification bugs, and they are far cheaper to catch at this stage than after the data is wrong.
. Build the connection
Authentication, requests, data mapping between the two systems, and error handling for the cases the documentation does not mention. Written as code you can read, not a black box.