Senior FinTech Backend Engineer — Payroll & Ledgers

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

Benefits offered by this job

Medical and dental benefits

401(k)

Catered lunches and dinners

Job summary

Simplex is hiring engineers to own the payroll and money-movement stack in a NY-based on-site role. You will design double-entry ledgers, idempotent payment execution, and reconciliations, while partnering with platform engineering and store owners who rely on accurate payroll data.

You will lead the financial correctness patterns and drive adoption across teams, including AI-guided coding and guardrails for money-touching code.

Qualifications

• 5+ years building production backend systems, preferably in TypeScript/Node.
• Fluency with transactional guarantees and idempotent processing.
• Deep PostgreSQL schema design and concurrent transactions.
• Experience with payroll, banking, or accounting integrations.
• Ability to design auditable, regulator-friendly ledgers and reconciliations.

Responsibilities

• Build our payroll product from the ground up with tax, withholdings, and filings integrations.
• Develop a bill-pay workflow for accounts payable within the platform.
• Embed bank accounts so clients access pygh revenues quickly.
• Own and harden QuickBooks integrations and month-end balance checks.
• Design ledgers for loyalty, gift cards, and deposits with correctness under concurrency.
• Define patterns for double-entry, reconciliation, and time-zone handling across teams.
• Scale AI-coding agents into the development workflow with safe guardrails.

Skills

TypeScript/Node

PostgreSQL

Financial systems

Idempotency

Ledger reconciliation

Payroll domain

Auditable ledgers

QuickBooks

AI tooling

Tools

Next.js

tRPC

Prisma

Vercel

ElastiCache

RDS

Job description

Simplex is hiring engineers to own the payroll and money-movement stack in a NY-based on-site role. You will design double-entry ledgers, idempotent payment execution, and reconciliations, while partnering with platform engineering and store owners who rely on accurate payroll data.

You will lead the financial correctness patterns and drive adoption across teams, including AI-guided coding and guardrails for money-touching code.