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Available for new projects

Cezary Siwadev

E-commerce and integrations developer. I connect stores to payment gateways, CRMs, ERPs and inventory, so orders, payments and data flow without manual work. 1,300+ projects since 2013.

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WooCommerce✦Shopify✦Stripe✦PayPal✦WordPress✦PHP✦REST API✦Webhooks✦Subscriptions✦
Payment gateways●CRM sync●ERP & inventory●Order automation●Custom checkout●Data migrations●High-risk stores●Headless●

( 01 ) — Intro

A store is only as good as what happens after the Buy button. I build the parts most developers avoid: payment gateways, custom checkouts, and the integrations that keep orders, stock, customers and invoices in sync between your site and the rest of your business, including high-risk stores (CBD, adult, research chemicals) that mainstream platforms turn away. Tested, logged and documented.

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Jobs completed on Upwork

$0M+

Earned with happy clients

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Hours billed

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Job Success · Top Rated Plus

( 02 ) — What I do

Where your store meets your systems.

01

Payments & checkout

Payment gateway integrations, custom checkout flows, one-off and recurring payments, and standalone payment pages. Tested in sandbox before a cent moves.

  • Gateways
  • Checkout
  • Webhooks
02

WooCommerce stores

Custom product logic, subscriptions, pricing and shipping rules, built so the shop stays fast and safe to update.

  • Subscriptions
  • Pricing
  • Shipping
03

API & system integrations

Syncs between your site and CRMs, ERPs, inventory, accounting or marketing tools. Orders, customers and stock stay in step automatically.

  • REST API
  • Webhooks
  • Scheduled sync
04

Shopify

Custom Shopify themes and app integrations for stores that have outgrown the defaults.

  • Themes
  • Liquid
  • Apps
05

Migrations & data sync

Moving stores between platforms and hosts without losing orders, customers or rankings, with redirects mapped before launch.

  • Orders
  • Customers
  • 301s
06

Store builds & care

The site around it all: custom WordPress themes from Figma, Core Web Vitals, security and long-term maintenance.

  • Figma → WP
  • Performance
  • Support

( 03 ) — How it works

From manual work to automatic.

  1. 01

    Map the flow

    Which system owns which data, what triggers what, and what happens when an API is down. Agreed before any code.

  2. 02

    Build in sandbox

    Test keys, a staging site and real sample data. You see it working before anything touches live payments or customers.

  3. 03

    Test the edge cases

    Declined cards, refunds, duplicates, timeouts and retries, all logged, so problems show up instead of failing silently.

  4. 04

    Launch & monitor

    A careful go-live with a rollback plan, then I stay around for fixes, new connections and the next phase.

( 04 ) — Selected work

A few of 1,300+.

All case studies →

( 05 ) — Kind words

What clients say.

★★★★★
“Cezary is probably one of the best developers I ever worked with. Not only he knows exactly what needs to be done but he is always making himself available.”
Upwork client
★★★★★
“Cezary is an excellent and disciplined developer capable of making the best decisions without the need of micro managing.”
Agency client
★★★★★
“The best experience with any developer I've had on Upwork. Everything was done right and ahead of schedule.”
Upwork client
★★★★★
“Hyper efficient, quick, and can tackle any request. Excited to work on the next project.”
Repeat client
★★★★★
“I tested 5 web developers and he was my favorite.”
Upwork client

( 06 ) — About

15+ years of shipping.

Computer science graduate, PHP programmer since 2008 (I started while still at university), and a full-time freelancer since 2013, working remotely with agencies and businesses in the US, UK and Europe. These days I focus on e-commerce, payments and integrations. English and Polish.

  • Top Rated Plus
  • 100% Job Success
  • AWS DevOps Professional
  • WordPress Multisite
  1. 2006→ 2010

    Computer Science, BSc

    Nicolaus Copernicus University

  2. 2008

    PHP Programmer

    Started alongside my studies. GoldenSubmarine (interactive agency, Warsaw & Poznań) and Juggernaut Technology (remote)

  3. 2013

    Full-time freelancer

    Upwork: 1,300+ jobs, 5,000+ hours, $1M+ earned

  4. Now

    E-commerce & integrations

    Payments, stores and API integrations for agencies and businesses worldwide

( 07 ) — Contact

Let's buildsomethinggreat.

cezary.siwa@gmail.com Hire me on Upwork ↗