Senior Software Engineer – Back End

Jobtailor; Seattle, California (WA, MO); On-site; USD 140,000 - 190,000; Full time

Job summary

Jobtailor is seeking an experienced backend engineer to own the payments domain on our kiosk platform. You will design and implement a pluggable payment SDK, support end-to-end flows from authorization to settlement, and build robust test/harnesses for new integrations.

You will lead architectural decisions around terminal abstractions and drive PCI‑DSS compliant practices. This role requires hands-on work with serial/USB protocols, various payment terminals, and cloud processing APIs, ensuring

Qualifications

• 6+ years back-end engineering with Java and Spring in a multi-module Maven/Java environment.

Responsibilities

• Own the payments domain end to end on the kiosk platform: authorize, capture, void, refund, reversal, settlement (EOD), and reconciliation.
• Re-architect the platform into a pluggable payment SDK: design plugin contract and lifecycle (discovery/registration, versioning, backward compatibility, capability negotiation, dependency isolation, per-integration configuration and secrets).
• Design a terminal abstraction spanning integrated, semi-integrated, cloud/REST processors and cash devices, enabling one model of coding for all transports.
• Build integration tests and certification harnesses for new/external integrations before touching real hardware.
• Set platform-wide patterns for money movement: idempotency, recovery, timeouts, health, concurrency, reconciliation.
• Design for PCI-DSS scope minimization: tokenization, P2PE, TLS/mTLS, key handling, audits.
• Drive architecture reviews, set technical direction for integration layer, and mentor engineers.
• Implement terminal integrations end to end, from protocol to high-level PayTerminal API.
• Work with serial (RS-232/USB-serial) and USB transports: port handling, reconnection, timing.
• Integrate cloud processors: retries, polling, reconciliation, webhooks.
• Debug live hardware: protocol traces, terminal logs, packet captures.

Skills

Java

Spring

Plugin architecture

SPI

PCI-DSS

Serial/USB protocol

Payment terminals

Job description

• Own the payments domain end to end on the kiosk platform: authorize, capture, void, refund, reversal, settlement (EOD), and reconciliation.
• Re-architect the platform into a pluggable payment SDK: design the plugin contract and lifecycle (discovery/registration, versioning and backward compatibility, capability negotiation, dependency isolation, per-integration configuration and secrets) on top of the existing PayTerminal SPI.
• Design a terminal abstraction that cleanly spans integrated vs. semi-integrated vs. cloud/REST processors and cash devices, so callers code to one model regardless of transport or vendor.
• Build the integration test and certification harness (extending the current mock-terminal approach) so a new or external integration can be validated, simulated, and regression-tested before it touches real hardware.
• Set platform-wide patterns for correctness in money movement: idempotency, transaction recovery and reversal, timeouts, heartbeat/health, concurrency, and reconciliation, in a system where double-charges and dropped captures are unacceptable.
• Design for PCI-DSS scope minimization: tokenization, P2PE, per-processor TLS/mTLS and certificate/key handling, so cardholder data stays out of in-scope services. Partner with security/QSA on audits.
• Drive architecture and design reviews, set technical direction for the integration layer, and mentor engineers building integrations.
• Implement new terminal integrations end to end, from byte-level protocol (framing, TLV/BMP/APDU, BCD/LLVAR, checksums, ACK/NAK state machines) up to the high-level PayTerminal API.
• Work directly with serial (RS-232 / USB-serial via jssc) and USB (usb4java) transports: port handling, event-driven reads, reconnection, and timing.
• Integrate high-level and cloud processor APIs (REST/SOAP, webhooks, semi-integrated terminal SDKs) with robust retry, polling, and reconciliation.
• Debug live hardware: protocol traces, terminal logs, packet captures, and vendor certification cycles.

Requirements

• 6+ years back-end engineering with strong Java (the platform is multi-module Maven/Java on Spring) and solid OOP and distributed-systems design.
• Demonstrated experience designing extensible / plugin / SPI-based architectures (ServiceLoader, OSGi, Spring plugin models, or public SDKs consumed by other teams or third parties).
• Hands‑on low‑level device and protocol experience: serial and/or USB communication and binary protocol implementation (TLV, BCD, bitmaps, length‑prefixed fields, state machines). EMV, ISO 8583, ZVT, or OPI a strong plus.
• Direct payment‑terminal / POS integration experience (Verifone, Ingenico, Adyen, Shift4, FreedomPay, SIX, Nepting, SiTef, Redsys, Worldpay, or comparable), and a clear understanding of integrated vs. semi-integrated models.
• Solid grasp of the card transaction lifecycle (auth, capture, void, refund, settlement, reversal) and PCI‑DSS boundaries, tokenization, and TLS/mTLS in production.
• Track record of technical leadership: leading designs, setting standards, and mentoring engineers.