Senior Software Engineer - Back End

About the role

Tillster is seeking a senior engineer to lead the evolution of our kiosk payment-terminal platform. You will re-architect our existing system into a modular, pluggable SDK to support over 40 integrations and ensure stable, versioned contracts for both internal and external developers.

Key facts

What you'll do

• Manage the end-to-end payment domain, including authorization, capture, void, refund, settlement, and reconciliation.
• Design a pluggable payment SDK with a focus on lifecycle management, versioning, and dependency isolation.
• Develop a terminal abstraction layer that supports integrated, semi-integrated, and cloud-based processors.
• Create certification and testing harnesses to validate integrations before hardware deployment.
• Establish standards for transaction recovery, idempotency, and concurrency to ensure financial accuracy.
• Implement security measures to minimize PCI-DSS scope, including tokenization and mTLS certificate management.
• Write code for terminal integrations, handling low-level protocols and serial or USB communication.
• Debug hardware issues using protocol traces, packet captures, and vendor logs.

Requirements

• 6+ years of back-end engineering experience.
• Proficiency in Java, specifically within multi-module Maven and Spring environments.
• Experience designing extensible architectures such as SPI models, OSGi, or public SDKs.
• Hands-on work with binary protocols, including TLV, BCD, bitmaps, and state machines.
• Experience with serial or USB communication protocols.
• Direct experience with POS or payment-terminal integrations like Verifone, Ingenico, Adyen, or Shift4.
• Knowledge of the full card transaction lifecycle and PCI-DSS compliance requirements.
• Proven ability to lead technical designs and mentor team members.

Nice to have

• Experience with cash automation, recyclers, or Vynamic Cash.
• Background in regional acquiring, multi-currency payments, or loyalty and wallet integrations.
• Familiarity with 3-D Secure, SCA, and fraud detection tools.
• Experience with vendor certification processes for acquirers and processors.

Skills & tools

• Java, Spring, Maven
• Serial (RS-232), USB, jssc, usb4java
• Binary protocols (TLV, BCD, ISO 8583, ZVT, OPI)
• Payment processing (Auth, Capture, Settlement, Reconciliation)
• PCI-DSS, TLS/mTLS, Tokenization

Practical notes

• Salary: $150,000 to $165,000 per year depending on experience.
• Benefits: Medical, dental, vision, FSA, EAP, and 401(k) participation.
• Time off: 15 days of PTO in the first year, increasing to 22 days thereafter, plus 10 paid holidays.
• Development: Includes tuition assistance and Udemy access.
• Visa: No visa sponsorship available.
• Residency: Must be based in San Diego, CA.
• Application: Principals only, no agencies.