Senior Software Engineer - Payment Integrations

On behalf of Softpay, TrinityHR is looking for a Senior Software Engineer – Payment Integrations. Does working for one of Europe’s fastest-growing fintech companies sound interesting to you? Are you keen to join an international team of highly dedicated people focused on dramatically changing how card payments are handled in-store? If so, you are in the right place. About Softpay and the product Softpay is a fintech company headquartered in Copenhagen that provides a software-based payment terminal. Their PCI MPoC-certified solution turns any Android or iOS phone or tablet into a contactless payment terminal (SoftPOS), supporting the shift away from dedicated hardware towards mobile, multi-purpose devices for payment and other in-store tasks. Since launching in 2021, Softpay havs gone live in more than 35 countries, working with major payment schemes, acquirers, and banks. With clients such as Matas, DSB, Salling, and Coop, and revenues doubling in the past year, they are growing fast. The team of 50+ passionate professionals, representing 20 different nationalities, is based in Copenhagen, where Softpay foster a flat, entrepreneurial culture that values initiative and creativity. The position Every acquirer, processor and card scheme that Softpay supports is connected to the platform through a payment integrator: a Java/Spring Boot microservice that translates Softpay transactions into the acquirer’s host protocol, handles key exchange and PIN/card-data security with our HSM, and carries the integration through certification and into production. The Integration Team owns these services end to end, from the first reading of a partner’s interface specification to production support once merchants are live. We are looking for a senior engineer to join this team and take ownership of new and existing acquirer integrations alongside other experienced integration engineers. In addition, we would like you to become the team’s go-to person on payment cryptography: our HSM client and key management. A colleague who can both build integrations and own the HSM side will be a major strength for the team, and the wider backend organisation will consult you on it. You will be based in the Copenhagen office, working closely with the backend, SDK and QA teams, and you will report to the VP of Projects. Tasks and responsibilities Acquirer and processor integrations Analyse partner interface specifications (ISO 8583 variants, Nexo/ISO 20022, REST/JSON and proprietary protocols), run the technical workshops with the partner and turn the outcome into a delivery plan.Design, implement and deploy new payment integrator services in Java/Spring Boot on AWS, covering the full transaction set: purchase, refund, reversal and advice handling, pre-authorisation and completion, tipping, surcharge and DCC.Configure the surrounding platform for each new processor: payment gateway routing, merchant/terminal administration, kernel data and public-key templates, and terminal key provisioning.Assist the team’s Certification Specialist with Level 3 and scheme certifications (Visa, Mastercard, Amex, Diners/Discover, Girocard and others) end to end and resolve findings down to individual EMV tags and host fields.Implement scheme and acquirer mandates and keep response-code mapping, SCA/soft-decline handling and reconciliation behaviour correct across integrations.Maintain the shared integration libraries, keep dependencies current (Spring Boot, TLS stack, etc.) and address security and compliance findings promptly.Own production health for your integrators: triage support cases, investigate host connectivity and timeout issues, run post-mortems and ship fixes. Payment cryptography and key management Maintain and extend our HSM client: implement new HSM commands and key-block operations as acquirer and platform requirements evolve.Implement and support PIN-block translation, DUKPT key derivation and MAC generation/verification (3DES and AES) in the transaction path.Support our iOS Tap to Pay and hardware-terminal initiatives with the key-management flows they depend on.Apply key-usage restrictions and secure logging practices, and contribute to the PCI DSS and MPoC documentation and evidence for our HSM and key-management processes.Be the team’s point of contact on cryptography questions for the backend, SDK and security teams. What we are looking for Required At least 5 years of professional Java backend development, with strong Spring Boot experience and services deployed to a public cloud (preferably AWS).Hands-on experience integrating with acquirer or processor hosts, or building payment terminal or payment gateway software, using ISO 8583 or nexo/ISO 20022.Working knowledge of EMV card payments: transaction flows, EMV tags and data elements, CVM, online/offline PIN and scheme rules.Comfortable running a partner integration end to end: reading specifications, asking the right questions, coordinating with external teams and driving certification.Strong troubleshooting skills in production systems, including reading logs, network traces and host protocol dumps.Attention to detail, a security mindset and a drive to deliver quality in a PCI DSS and MPoC environment.Excellent written and spoken English; you will work daily with international partners. Desired Experience with Visa/Mastercard Level 3 or other scheme certifications, and with specific domestic schemes (girocard, Dankort, Bancontact, Cartes Bancaires or similar).Practical experience with payment cryptography and HSMs: key blocks, key exchange (TR-31/TR-34), PIN-block formats, DUKPT and MAC, and how they are used in a PCI environment.Experience with payment-HSM vendor command sets and key-block formats (Atalla/AKB, Thales, Utimaco or comparable) and with cloud-hosted HSM services.Experience from owning a system end to end. Location The role is based on-site at our office in Copenhagen (Østerbro). Why Softpay? Work in a fast-growing company in payments and fintech, with a product that is live with major retailers, acquirers and partners across Europe and beyond.Join a highly skilled team of senior professionals and take real ownership of integrations from first workshop to live merchants.A flat organisation with few formal procedures, where you can both influence and learn.Competitive salary and benefits, including health insurance, daily subsidised lunch and company events.A good office location in Copenhagen, which includes an excellent espresso machine.A company financially backed by a series of experienced entrepreneurs and investors.