Founding Engineer

About the Role

This is a security-focused product handling real money, and Sebastian currently owns everything from smart contracts and backend to app, infra, and security/audits; you'll be taking meaningful chunks of that off his plate.

Very open to different combinations. Full-stack is an easy win right now. A super focused backend engineer with little

product experience would also be a big win. "Happy to pitch in on product and UI" is also a plus, but not a requirement.

In order of priority:

1.Security expert with some experience in smart contracts would be the top, although there is a higher bar for this (and more equity on the table) and it is not the initial focus of my recruiting search as I'm complementing this with external security firms in the short term while I build leverage to go hire this person

2.Full Stack

3.Backend

4.Product/Frontend

Not really looking for infra/devops at this time. Hoping to find a security person who is proficient at this later.

Key Responsibilities

Backend & integrations

Design and build backend services that connect custody, fiat rails, policies, and operational workflows.

Implement and maintain APIs and services that power ACH, wires, cards, permissions, AML/compliance workflows, and reporting.

Smart contracts & security-sensitive logic

Implement and review Solidity smart contracts, focusing on correctness, safety, and upgradeability.

Contribute to threat modeling, security reviews, and audit/vendor management under Sebastian's supervision.

Product & full-stack work

Collaborate on the design and implementation of customer-facing applications (currently Dart/Flutter on the client).

Help translate user and operational needs into product and UX decisions, especially around permissions, approvals, and money flows.

Security & audit participation

Own parts of the audit/security review process for your areas of the stack, coordinating with external security firms.

Build systems and internal processes with a security-first mindset appropriate for handling customer funds.

Tech stack

Reins' current stack includes:

Backend: TypeScript

Smart contracts: Solidity

Client applications: Dart / Flutter

There are no hard "must have" technologies, but experience or strong interest in these areas is helpful.

Requirements

Roughly 3-6 years of professional experience, with openness to high-potential 0-3 years if there is strong

evidence of capability and ownership.

Prior early-stage startup experience or very strong ownership in a small team (especially in fintech or infrastructure)

Solid backend engineering skills, comfortable designing and implementing production services and integrations.

Bonus Skills

* Experience in fintech (payments, neobanks, custody, treasury, cards) is even more valuable than pure crypto experience.

* Prior work with Solidity or other smart contract languages, ideally combined with backend experience.

* Full-stack capabilities (comfortable jumping into frontend/product/UI in addition to backend and contracts).

* Experience with audits, security reviews, threat modeling, or working closely with external security vendors.

* Crypto/web3 familiarity or curiosity; prior stablecoin or DeFi experience is a plus but not required.

* Smart contracts guy who is good at backend + a product engineer that is full-stack and can also touch the backend is the ideal configuration