Full Stack Engineer

Payment Gateway Developer

Location: Jakarta · Hybrid 3–4 days in office Reports to: Founder / Engineering lead Compensation: Competitive cash base + performance bonus Start: As soon as available

About Xellar

Xellar is a financial platform providing API-based payment and money movement infrastructure. We operate across multiple regulated entities and serve customers across Southeast Asia and beyond.

The role

We are hiring a developer to own our payment gateway layer — the integrations that connect our platform to banks, payment networks, and gateway partners, and the operational discipline that keeps money moving 24/7.

Payments is a domain where the happy path is easy and everything else is the job. Timeouts that may or may not have settled. Callbacks that arrive twice, late, or never. Partner sandboxes that behave nothing like production. Reconciliation breaks at 2am on payday volume. You will be the person who owns all of it — and who builds the systems so that less and less of it needs a person at all.

This is a high-ownership seat. You will not be one of forty engineers on a payments team. You will be the engineer on this layer, with direct access to the founder and the authority to fix things properly.

What you'll own

Partner integrations. Build and maintain integrations with banks and payment partners across the channels our businesses run on — QRIS, virtual accounts, e-wallets, disbursements, cards. Take each one from sandbox to certification to production, and keep it healthy after launch.

Reliability of money movement. Design for the failure modes that define payments: idempotency, retries, duplicate callbacks, partial failures, stuck transactions. A payment that silently disappears is the worst bug we can ship — your job is to make it structurally impossible.

Monitoring and incident response. Own the dashboards and alerting for transaction success rates, latency, and partner uptime. When a channel degrades, you detect it before the partner tells us — and long before a customer does.

Reconciliation support. Work with finance to make sure every transaction can be matched: clean transaction states, complete logs, settlement files parsed and loaded. When the numbers don't tie, you can trace any transaction end-to-end in minutes.

Partner technical relationships. Be the technical counterpart to our partners' integration teams — spec reviews, certification calls, production escalations. You read a partner API doc once and immediately see where it will hurt.

Internal tooling. Build the admin tools that let operations resolve stuck transactions, requery statuses, and trigger refunds safely — without paging you.

What we're looking for

We index on raw intelligence and operating tempo over years on a CV. The best payments engineers we have met share a small number of qualities:

• Precision under ambiguity. Partner docs are wrong, sandboxes lie, and the spec is whatever production actually does. You verify rather than assume, and you never mark something done that you haven't seen work end-to-end.
• Distributed-systems instincts. You reason naturally about idempotency, exactly-once vs at-least-once, race conditions, and what happens when a request times out mid-flight. You don't need these explained; you design for them by reflex.
• Operating velocity. You ship integrations in days, not months. You close loops. You don't go quiet. When something breaks, you communicate first and fix fast.
• Strong in our stack: JavaScript/TypeScript and Go. Our backend runs on Node (JS/TS) and Golang — you should be strong in at least one and productive in both. Comfortable with SQL, queues, and webhook-driven architectures.
• Ownership temperament. You treat a degraded channel as your problem at any hour, then build the automation so it never wakes you again. You'd rather write the runbook than follow one.
• Located in or willing to relocate to Jakarta. This is a hybrid in-office role.

If you have eight years at a payment gateway or switching company, we will absolutely talk. But if you are two years out of school, exceptionally sharp, and obsessed with how money actually moves, we want to talk to you even more.

Bonus points

• Prior experience working at a payment gateway — you've lived the switcher/acquirer/PG world and know how certification, settlement, and partner escalations actually work
• Web3 development experience — smart contract interaction, wallet infrastructure, stablecoin transfers, or building against EVM chains
• Direct experience integrating QRIS, virtual accounts, or disbursement APIs with Indonesian banks or PJPs
• Familiarity with ISO 8583, ISO 20022, or settlement file formats
• Experience with reconciliation systems or ledger design
• Exposure to regulated environments and what audit-ready logging looks like