About
The engineer behind Invocation
Independent, production-grade delivery since 2015 — from Belgrade, Serbia, for clients worldwide.
I'm Andrej Dragojevic. I build the platforms money runs through — two-sided marketplaces, digital wallets and escrow, payout rails, subscription billing, internal accounting tools — from an empty repository to production, and I'm the engineer companies call when one of those systems can't be allowed to fail: billing migrations where every mistake costs real revenue, marketplaces holding other people's money, fintech platforms that have to stay up while being rebuilt.
The defining project so far: I led the migration of Babbel's recurring billing — $100M+ in recurring revenue — from Adyen to Stripe (2024–2026), finished with zero downtime. Before that, I built GigSocial's creator marketplace from an empty repository to thousands of monthly transactions and global payouts — escrow, wallets, disputes, card and ACH payouts, all designed and written from the first line — led the modernization of eifas's fintech platform in Germany, and shipped booking and marketplace platforms across Europe and the US. Today that work is sold as fixed-scope builds: the money layer of a marketplace, wallets and escrow, or a whole platform in phases — handed over, owned by you.
I'm a Stripe Certified Professional Billing Architect — the credential is public and linked, and you're welcome to verify it. When your revenue runs through code I wrote, that piece of paper matters.
The AI part isn't a pivot. It's how I work.
I build and operate Antrix OS, my own automated engineering platform: AI tooling orchestrated across Claude Code, Codex, and automated review loops, picking up GitHub issues, implementing them, and cross-checking the work — with me as the senior engineer in the loop. It's why a solo engagement with me delivers at a pace that used to need a team.
That operating experience is what I sell in automation engagements: automations and LLM integrations engineered with the same discipline as a billing system, because I've learned the failure modes on my own infrastructure first.
I also ship my own products. Count21, a blackjack strategy trainer, is a paid SaaS I built solo — product, brand, UI, infrastructure, Stripe Billing with subscription and lifetime tiers, and an AI-driven content pipeline for its marketing. ArenaMaster, a World of Warcraft rankings and character-profiles platform, still serves its competitive community eight years after launch — 10,000+ players, a companion addon with 2.4M+ downloads, recently rebuilt top to bottom without stopping it. And eSalon, a multi-tenant scheduling SaaS I own and operate — staff, shifts, QR bookings, notifications, and subscription billing — runs salons day in, day out. Owning products end to end keeps me honest about what shipping really takes. The AI side of my work — Antrix OS, automation systems, and what I'm building with them — lives at antrix.dev.
How I think about the work
Production is the only benchmark
Demos are easy. I measure work by what survives real customers, real money, and real load — and I've kept that bar for a decade.
Numbers over adjectives
$100M+ in recurring revenue migrated between providers with zero downtime. If I can't quantify it, I won't claim it.
Honest scoping
If your project doesn't need me — or doesn't need building at all — I'll say so in the first call. Reputation compounds better than billable hours.
Bleeding edge, deliberately
I run automated AI systems in my own work every day, so when I bring automation into yours, it's from operating experience — not from a blog post.
Core stack
- Ruby on Rails
- Next.js
- React
- PostgreSQL
- Stripe
- Adyen
- AWS
- Azure
- Terraform
- Claude Code
- Codex
- MCP
Bigger than one engineer?
When a project needs more hands — design, mobile, e-commerce, marketing pages — I bring in a small delivery network of specialists I've worked with for years. Same accountability, one point of contact: me.
Meet the networkSounds like the kind of engineer you need?
Tell me what you're building. I read every message myself.
I reply within one business day. Now booking new engagements.