Alt.xyz

Senior Fullstack Engineer, Payments

United States full-time Senior $140,000 - $180,000
full-time Senior level Technology & IT Salary listed Curated
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About the role

Alt is unlocking the value of alternative assets, starting with the $5 B trading-card market. We let collectors buy, sell, vault, and finance their cards in one place and we are backed by leaders at Stripe, Coinbase, Seven Seven Six, and pro athletes like Tom Brady and Giannis Antetokounmpo. Our next frontier is real-time pricing at scale—the Alt Value that powers every trade, loan, and product on the platform.

We’re looking for a Senior Fullstack Engineer who wants to build the financial engine of our platform. You’re not just building a checkout flow; you’re powering the liquidity that makes this marketplace work. You’ll join a high-impact team responsible for our custom double-entry ledger, payment provider integrations, and our core lending products.
If you have a "measure twice, cut once" mindset for backend integrity but still move with a bias toward action on the frontend, you’ll thrive here.
What You’ll Do Here:

Engineer Financial Integrity: Build and maintain our custom-built double-entry ledger system to ensure every cent is accounted for across the platform.

Own Lending Infrastructure: Design and scale our lending products—from the logic of credit disbursements to the automated lifecycle of loan management.

Architect Integrations: Design and implement robust integrations with payment gateways and banking partners, ensuring 99.99% reliability and seamless reconciliation.

Own the UX of Money: Create high-trust user interfaces for payments and lending that make complex financial actions feel simple, transparent, and secure.

Balance Rigor with Speed: Make thoughtful trade-offs between rapid feature shipping and the uncompromising correctness required for financial systems.

Be a Multiplier: Level up the team through rigorous code reviews, technical documentation, and mentorship.

This is a perfect fit if you…

Are Obsessed with Correctness: You understand that in payments, "mostly working" is a failure. You think deeply about idempotency, race conditions, and data consistency.

Think Like a Product Owner: You don't just build a "pay button"; you understand the flow of funds and how to communicate financial status clearly to the user.

Love Building Infrastructure: You’re energized by the challenge of building a ledger or a lending engine from the ground up.

Are Pragmatic: You know when to build a custom internal solution and when to leverage a third-party API to get the job done.

What You Bring to the Table:

5+ years of experience with a heavy focus on backend systems (Python, Postgres, AWS) and a proven ability to build modern frontends (React, TypeScript).

Fintech or Payments experience: You’ve worked with ledgers, payment processors, or lending products and understand the complexities of moving money.

Database Mastery: You are an expert in SQL and relational database design—you know how to write a transaction that won't fail under load.

Fullstack Ownership: A track record of taking a complex financial feature from a technical design doc all the way to a polished UI in production.

Bonus: Experience with distributed systems, credit/risk modeling, or the alternative asset space.

What You’ll Get From Us:

A seat at the table to help shape the future of Alt and the alternative asset space

Autonomy and ownership on projects that matter

$100/month work-from-home stipend

$200/month wellness stipend

WeWork office stipend

401(k) retirement benefits

Flexible vacation policy

Generous paid parental leave

Competitive healthcare benefits, including HSA, for you and your dependent(s)

Base salary range: $140,000-$180,000, plus equity. Offers may vary based on experience, location, and other factors.
Originally posted on Himalayas

Interview prep

Walk in with sharper answers.

Use this as a quick practice sheet before you speak with the employer.

Senior
Technology & IT API integration Finance Javascript MySQL Python Senior level

Likely questions

  1. Tell us about work you have done that is close to the Senior Fullstack Engineer, Payments role.
  2. How would you approach your first 30 days at Alt.xyz?
  3. Which of API integration, Finance and Javascript have you used recently, and what did it help you achieve?
  4. How have you led people, improved a process, or made a hard decision in a previous role?
  5. How do you handle busy days, changing priorities, or pressure at work?

Prepare before the call

  • A recent example that proves your experience with API integration, Finance and Javascript.
  • One short story with a problem, your action, and the result.
  • Two examples that show the strengths listed on your CV.
  • A clear reason why this role and company interest you.
  • Your availability, preferred work style, and salary expectations.

Ask them

  • What would success look like in the first 90 days?
  • What are the main problems this hire should help solve?
  • How does the team give feedback and measure good work?
  • What does a normal working week look like for this role?
Practice line

I am interested in the Senior Fullstack Engineer, Payments role because I can bring practical experience in API integration, Finance and Javascript, learn the team quickly, and contribute to the outcomes Alt.xyz needs from this hire.

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