About
The engineer behind Invocation
Independent, production-grade delivery since 2014 — from Belgrade, Serbia, for clients worldwide.
I'm Andrej Dragojevic. For over ten years I've been the engineer companies call when the system can't be allowed to fail: billing migrations where every mistake costs real revenue, marketplaces holding other people's money in escrow, fintech platforms that have to stay up while being rebuilt.
The defining project of that career so far: leading the migration of Babbel's recurring billing — hundreds of millions in recurring revenue — from Adyen to Stripe with zero downtime. Before that, I built GigSocial's influencer marketplace from an empty repository to thousands of monthly transactions and global payouts, led the modernization of eifas's fintech platform in Germany, and shipped booking and marketplace platforms across Europe and the US.
I'm a Stripe Certified Professional Billing Architect — one of the few independent engineers holding Stripe's highest billing certification. 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 agentic engineering platform: multiple AI agents orchestrated across Claude Code, Codex, and automated review loops, picking up GitHub issues, implementing them, and reviewing each other's 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 AI 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 arena partner finder, still serves its competitive community years after launch. Owning products end to end keeps me honest about what shipping really takes. The AI side of my work — Antrix OS, agentic 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
Hundreds of millions in client revenue migrated and processed without incident. 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 agentic AI systems in my own work every day, so when I bring AI 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.