Senior Software Engineer (Builders Welcome)

Job Description

Most engineering job descriptions read like a checklist. This one is different. At pmtbox (“Payment Box”), we’re building a fintech platform that helps businesses manage their payments-related risk, fraud, card declines, chargebacks, and related processes intelligently. We’re a VC-backed fintech with a small team, over 1,000 active clients, and big ambitions, and we’re looking for engineers who want to build things, not just complete tickets. If you’ve spent your career in a dev shop where product managers feed you Jira tickets all day … this role might feel very different. We’re looking for engineers who:

• Build things on their own
• Are comfortable working within systems and workflows and thinking of ways to improve processes
• Use AI as a force multiplier in your development workflow
• Enjoy solving complex problems that span the layered architecture of web applications

What You Might Work On

You’ll be building real products alongside founders, including a technical co-founder with deep industry experience and expertise, and a small, high-performing engineering team. Expect to:

• Design and build product features within a structured Rails codebase using a tests-first approach in a CI/CD environment
• Improve internal tooling, automation and data workflows
• Build integrations with mid-market and enterprise clients
• Use and refine AI-assisted development workflows and tools
• Contribute to architectural decisions as our platform's data model and intelligence layer grows

How Our Engineering Team Works

This is not a role where everything is already defined but it’s also not greenfield. You’ll be building within established patterns and codebases. Our engineering team is small and deliberately so. We currently support over 1,000 active clients across a Rails/Postgres stack with AI-assisted development workflows integrated into daily work.

We maintain a TDD-first codebase with CI pipelines, and structured project context that keeps both humans and AI tools oriented. This isn't a “move fast and break things” environment; it's a “move fast because the guardrails are good” kind of environment. You'll have real autonomy within well-defined boundaries: a tested codebase, clear architectural patterns, and context documentation that means you can ship independently without waiting for someone to unblock you.

What We’re Looking For

We care less about years of experience and more about how you think and what you’ve built. You might be a great fit if you:

• Have experience with PHP, Python, or Ruby
• Can show things you’ve built yourself: GitHub projects, side tools, automation scripts, or personal software projects are great to share with us
• Think beyond coding and into systems and workflows
• Are curious about how AI changes how software gets built

We use AI-assisted development workflows daily as part of our core infrastructure. We’re looking for engineers who’ve already started building their own workflows and can demonstrate: :

• A project where AI assistance measurably changed your development speed or approach
• How you support AI workflows with other scripts or tools when it doesn’t work to one-shot it
• Knowledge of how to feed data into the AI so that it can deliver quality results
• A workflow you built to validate the output from an AI workflow
• A workflow where you learned that AI confidently lied to you and what you did to build around that

We want engineers who understand where AI helps the workflows and where it breaks down, not just the latest tools and methods

The Kind Of Engineer Who Thrives Here

You’ll probably enjoy this role if you:

• Like solving ambiguous problems
• Prefer building over attending meetings
• Have shipped things without being told exactly what to do
• Enjoy improving systems and processes
• Want real ownership of what you build

Our Stack (and What We’re Exploring)

Our team works across modern backend technologies and is constantly experimenting with better tools and workflows. Current and emerging technologies include:

• Ruby / Rails
• Postgres
• AI-assisted development workflows
• Modern cloud infrastructure

We’re far more interested in how you solve problems than whether you’ve used a specific framework.

Why Join pmtbox

• Early-stage fintech with real momentum and VC-backing by Tandem Ventures (Founders of fintech unicorns Divvy, Finicity, etc.)
• Small team, high ownership
• Work on meaningful ecommerce infrastructure
• Build alongside founders and experienced operators in a five-days-a-week in-office culture
• Competitive compensation and benefits package including enterprise-level medical, dental, vision, 401k, and generous time off