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Node.js Intern - Payments & Billing Services
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Where you land
Billing code is unforgiving, which makes it a very good place to learn. MailerMen bills employers per job post and per credit pack, and the service that does it is a compact Express application talking to a payment gateway, a PostgreSQL ledger and a nightly reconciliation job. This six month internship puts you inside it.
Responsibilities in practice
Early on you write Jest tests for the existing invoice calculation, which turns out to be the fastest way to learn the rules nobody wrote down. Then you build the webhook handler for failed and refunded payments, add an append only ledger table so balances are never mutated in place, and produce a reconciliation report that flags every mismatch between our records and the gateway.
Why six months and not two
Money bugs surface slowly. Staying long enough to watch a full billing cycle, a quarter close and one genuine customer dispute teaches things a short project cannot. You work from the Mumbai office on Tuesdays and Wednesdays, and a senior engineer reviews every change that touches the ledger before it merges. Final year students and recent graduates are equally welcome here.
Responsibilities
- Write Jest tests around the existing invoice calculation to document its rules
- Build webhook handlers for failed, refunded and disputed payment events
- Design an append only ledger table so account balances are never mutated in place
- Produce a nightly reconciliation report comparing our ledger against gateway records
- Add idempotency keys to every write path that touches money
- Support the finance team through a quarter close and fix what the close uncovers
Requirements
- Final year student or recent graduate; we do not expect any work experience
- A methodical approach to code, where correctness matters more than speed
- Node.js and Express basics plus enough SQL to write a grouped report query
- Interest in payments, ledgers or accounting ideas, even if only from reading
- Available for two office days a week in Mumbai across the six months
Skills
Benefits
- Six months of mentoring from the engineer who owns the billing service
- Real ownership of a production ledger feature
- Completion certificate and a detailed written reference
- Priority consideration for junior backend openings