Senior Backend Developer (High-Throughput APIs)

Quick Facts

• Role: Senior Backend Developer (High-Throughput APIs)
• Domain: Payments / Fintech
• Work focus: Scalable backend services and B2B API development
• Location/Model: Remote (candidates based in Portugal)
• Duration: 6–12 months

Description

You will design and develop highly scalable backend services and B2B APIs for a core financial processing platform. The work focuses on handling very high transaction volumes, owning complex technical challenges end-to-end, and ensuring performance, scalability, reliability, and security. You will also modernize existing PHP and Java modules toward Go and implement observability and resilient asynchronous processing.

Responsibilities

• Design and develop scalable backend services and B2B APIs
• Build systems for very high transaction volumes
• Own complex technical challenges from design to production
• Design APIs, services, data models, and distributed systems for scalability and reliability
• Write clean, maintainable, testable, production-ready code
• Optimize SQL queries and indexes for relational databases
• Identify and resolve performance bottlenecks across applications, databases, and systems
• Design asynchronous processing and concurrent workloads
• Migrate/modernize legacy PHP and Java modules toward Go
• Implement retry, recovery, and dead-letter mechanisms
• Add observability via structured logging, metrics, tracing, and production monitoring
• Apply security principles across API and service design and implementation
• Contribute to automated testing, CI/CD, containerization, and production deployments
• Review code and provide meaningful feedback on technical designs

Requirements

• Strong proficiency in PHP and Java
• Experience designing and developing backend systems
• Strong understanding of relational databases and SQL optimization
• Experience with high-transaction-volume systems
• Familiarity with asynchronous processing and concurrent workloads
• Ability to contribute to system design, architecture, and security
• Strong problem-solving skills focused on performance, scalability, and reliability
• Professional fluency in English
• French fluency is a plus

Benefits

Opportunity to contribute to an evolving core financial processing platform in the Payments/Fintech space.