Senior Software Engineer - Cards

As the story goes, in 1949 Frank McNamara finished dinner at a New York restaurant and found he'd left his wallet in another suit. His fix was a card that let members eat now and pay later. That card became Diners Club, widely credited as the first multipurpose charge card. It was a piece of cardboard and a promise: the restaurant trusted the card, the card trusted the member, and someone had to make sure the money actually moved.

More than seventy-five years later, the promise hasn't changed, but the machinery has. When a Mercury customer taps their card, the request goes from the merchant's terminal through an acquirer and a card network to us. In a fraction of a second, we check the balance, apply the customer's spend controls, screen for fraud and say yes or no. After that comes clearing, settlement, disputes and reporting, and every cent has to reconcile.

Cards are the way Mercury customers spend money. The Cards Integration team owns the whole Mercury card, not just the swipe: issuance, physical card shipping, spend controls, lifecycle management, authorization, money movement, settlement and reporting, and the infrastructure underneath. We're a full-stack team, and our job is to make the Mercury Debit and IO cards reliable, correct, useful, and innovative.

We're looking for a Senior Software Engineer who thinks deeply about systems architecture, cares about the customer experience, and will dive into any problem to move the team forward. We value high ownership, working in pairs and teams rather than alone, and attention to detail. Those matter when you run systems held to four nines of reliability, and everyone around you will care about them too.

In this role, you will

• Lead projects from idea to tech spec to implementation to launch, working with your PM, EM, tech lead, and teammates at each stage. When you lead a project, it's yours to see through.
• Learn how debit and credit cards actually work under the hood (authorization, clearing, settlement, disputes) and use that knowledge every day.
• Build features across the stack, from the card experiences customers use to the backend systems that move money.
• Help keep our operations excellent. Our systems are some of the most observable at Mercury, and with great observability comes great responsibility.
• Mentor other engineers and raise engineering quality through design reviews, code reviews, and collaboration.
• Work with product, design, operations, risk, compliance, sales, and many other teams.

You should

• Have strong full-stack experience, a product mindset, systems thinking, and a knack for getting things across the line.
• Have made architectural decisions on complex systems, and be able to explain your reasoning and the trade-offs.
• Be excited to put new features in customers' hands, and care just as much about keeping existing ones working like a charm.
• Care about correctness in systems where failure has real financial consequences.
• Communicate clearly, handle ambiguity well, and enjoy mentoring others.
• Be comfortable with our tech stack (Haskell and TypeScript) or be ready to learn.
• Bonus: experience in fintech, payments, or card issuing.

We encourage you to try our demo site if you're interested in applying for the role.

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