Open to opportunities

Juan Millan

@juanmillan

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Senior Full-Stack Engineer improving legacy systems and payments.

Ireland

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What I'm looking for

I seek roles improving reliability and performance of large systems, focusing on payments, maintainability, mentorship, and cross‑functional collaboration in distributed teams.

I am a Senior Full-Stack Engineer with over a decade of experience improving legacy systems, payment platforms, and enterprise software to make technology effectively invisible to users.

I specialize in payment integrations and performance: I have worked on platforms handling millions in transactions, led Laravel upgrades (5→12), containerization with Docker, and infrastructure changes that reduced deployment time by 60%.

I build reusable libraries and backend architectures for multi-tenancy, payment processing, and digital twin infrastructure, and have optimized payment pipelines using tools like Tideways and XHProf to reduce latency and increase throughput.

I enjoy mentoring and knowledge transfer—I've delivered practical curriculum through Square1 Academy—and I thrive working with distributed teams across continents to untangle legacy code, reduce technical debt, and improve long-term maintainability.

Experience

Work history, roles, and key accomplishments

Current

Senior Full Stack Developer

Current

Square1

Jul 2020 - Present (5 years 6 months)

Led Stripe and PayPal integrations for enterprise payment platforms handling millions in annual transactions; upgraded Laravel from v5 to v12 and implemented Docker containerization, reducing deployment time by 60%.

Laravel PHP Docker Payments PayPal Containerization CI CD Mentoring

Development Engineer

Evertec

Jan 2019 - Dec 2019 (11 months)

Used Tideways and XHProf to identify and resolve bottlenecks in payment pipelines, reducing processing latency and increasing transaction throughput across high-volume flows.

Performance Profiling Tideways XHProf PHP Payment Processing Throughput Linux

Backend Developer

ENGworks

Feb 2016 - Jan 2019 (2 years 11 months)

Built database-backed solutions and backend architecture for digital twin and facility management platforms, delivering automated maintenance alerts, workorder systems, and compliance reporting.

Database Design MySQL PostgreSQL APIs PHP Backend Automation

Software Developer

INSCRA S.A.S

May 2012 - Apr 2014 (1 year 11 months)

Provided technical support and modernized legacy accounting systems, improving code quality, system architecture, and long-term maintainability while reducing technical debt.

Accounting Systems PHP Refactoring Technical Debt Reduction