Senior FinTech Backend Engineer: Payroll & Ledger, Equity

Simplex.; New York (NY); On-site; USD 220,000 - 300,000; Full time

Benefits offered by this job

Equity

Medical and dental benefits

401(k)

Catered lunches and dinners

Job summary

Simplex., a Series A point-of-sale software company in NYC, is building payroll and financial systems that move money with precision across multi-location stores. You will own core ledger, accounting sync, and money-movement rails, partnering with Platform Engineering and store owners.

You will craft double-entry ledgers, idempotent flows, and reconciliation jobs while leveraging AI-assisted coding as a core workflow element. This role is on-site in NYC with substantial ownership.

Qualifications

• Background in Fintech or payment ecosystems (Stripe, Block/Square, Plaid, etc).
• 5+ years building production backend systems.
• Experience with transactional guarantees: idempotency, atomicity, retries.
• Deep PostgreSQL knowledge: schema design, concurrent transactions, fast queries.

Responsibilities

• Build payroll product from the ground up using platform data, tax withholding, payments, and filings integrations.
• Develop bill-pay features enabling one-click accounts payable in platform.
• Embed bank accounts into the OS so customers access card processing revenues quickly.
• Own and harden accounting integrations (QuickBooks today).
• Design and maintain ledgers behind loyalty, gift cards, and deposits with correctness and auditability.
• Establish financial-correctness patterns adopted by other teams (double-entry, reconciliation).
• Leverage AI coding agents to accelerate delivery with safety guardrails.

Skills

Backend engineering

TypeScript/Node.js

PostgreSQL

Financial systems

AI agents integration

Payroll systems

Tools

Next.js

tRPC

Prisma

Vercel

RDS/RDS Proxy

ElastiCache

Job description

Simplex., a Series A point-of-sale software company in NYC, is building payroll and financial systems that move money with precision across multi-location stores. You will own core ledger, accounting sync, and money-movement rails, partnering with Platform Engineering and store owners.

You will craft double-entry ledgers, idempotent flows, and reconciliation jobs while leveraging AI-assisted coding as a core workflow element. This role is on-site in NYC with substantial ownership.