Senior Software Engineer - Back End

Role: Senior Software Engineer - Back End Hybrid Role, MUST BE BASED IN SAN DIEGO, CA About Tillster Tillster, headquartered in the USA, is the global leader in digital ordering and customer engagement solutions. For over a decade we have developed revolutionary self-service, ordering and payments solutions - for mobile, tablet, online, kiosk, call center, and more - creating personalized interactions based on consumer preferences, language, and currency. Our platform is compatible with 15+ unique POS systems, representing over 90% coverage in multi-unit restaurants. We offer one platform; one scalable, enterprise class solution - to create world-class digital engagement solutions. Our mission and passion are one in the same: Empower restaurants and consumers to engage and transact anywhere, anytime, and from any device - one consumer at a time, one order at a time, billions of times over. In doing so, together we are transforming e-commerce in restaurants and make the till grow for Tillster and our customers. About the Role We are looking for a Senior Engineer (bordering on Architect) to own and evolve the payment-terminal platform behind our kiosks: a layer of 40+ integrations spanning card-present terminals, semi-integrated and cloud processors, and cash automation. You will re-architect this into a modular, pluggable SDK so internal teams and external/third-party developers can build new integrations against a stable, versioned contract without forking the core, and you will stay hands-on, implementing new integrations down to the wire-level protocol. What You'll Do (architecture and ownership) 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. What You'll Do (hands-on, low to high level) 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. About You (required) 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. Nice-to-haves Cash automation and recyclers (Vynamic Cash or similar), end-of-day and reconciliation tooling. Regional acquiring experience (LatAm, EU, Middle East) and multi-currency payments. Loyalty, stored-value, gift, or wallet (Apple Pay / Google Pay) integration. Vendor certification experience with acquirers and processors; 3-D Secure / SCA, fraud/risk tooling. Thriving at Tillster As a member of Tillster, you will embody our core values:

• Put Customers First: Prioritize the needs and satisfaction of our customers in all decisions and actions appropriate to Tillster's stage of development, resources, and stated goals.
• Collaborate: Work together effectively, leveraging diverse perspectives to achieve common goals.
• Innovate: Embrace creativity and pursue new ideas to drive progress and improvement.
• Operate from Data: Use strong critical thinking skills to make informed decisions based on accurate and relevant data.
• Drive Results: Focus on achieving tangible outcomes and delivering high performance.
• Own It: Take responsibility for your actions and the success of your work.
• Be Passionate and Have Fun: Bring enthusiasm to your work and enjoy the journey.

The Interview Process Recruiter interview with a Talent Acquisition Specialist Interview with Hiring Manager Technical Assessment Interview with our Kiosk-Payment Team Final Interview-Head of Kiosk Pay and Benefits (USA) Salary is $150,000 - $165,000 DOE Health Benefits: All full-time, regular employees and their dependents are eligible for medical, dental, vision and FSA benefits. Additional health benefits include Healthcare and Dependent Care reimbursement programs, Employee Assistance Program ("EAP") and Optum Care 24-hour confidential medical counseling services. Holidays: The company observes ten (10) paid holidays per calendar year. Paid Time Off (PTO): Full-time, regular employees earn 15 days of PTO in the first 12-months of continuous service, and 22 days in subsequent years. Eligible part-time employees earn pro-rated PTO. Retirement: Effective with your employment start date, you will be eligible to participate in the 401(k) Plan. Education, Learning & Development: We offer college tuition and education assistance programs; Udemy Learning courses; and ongoing learning and development opportunities. Local Candidates Only No Visa Sponsorship Principals only - no Agencies or calls please Tillster