About the Role
Apex Technologies Ltd is a fast-growing FinTech company building the next generation of payments infrastructure for enterprise clients across Europe. Following a successful Series B funding round of £45 million, we're scaling our engineering team significantly and are looking for an experienced Senior Software Engineer to lead a core backend engineering squad.
This is a high-impact role where you'll have genuine ownership over architectural decisions, mentoring responsibilities, and the opportunity to directly shape how millions of transactions are processed every day. You'll work in a truly agile environment with a talented team that cares deeply about quality, reliability and developer experience.
The role is based at our London office in Shoreditch, operating on a flexible hybrid model — three days in the office and two days remote per week.
Key Responsibilities
- Design, develop and maintain cloud-native microservices using Java and Kotlin on AWS infrastructure
- Lead technical design discussions, architecture reviews and code reviews within your squad of 5–7 engineers
- Drive improvements to system reliability, scalability and performance across high-volume payment processing flows
- Champion engineering best practices — TDD, continuous integration, observability and documentation
- Collaborate closely with product managers, designers and QA engineers to deliver features end-to-end
- Mentor junior and mid-level engineers, supporting their professional development and code quality
- Contribute to hiring — including technical interviews, pair programming assessments and hiring feedback
- Participate in on-call rotation for production incidents (approximately 1 week in 6)
Required Skills & Experience
To be considered for this role, you will need to demonstrate:
- 5+ years of professional software engineering experience, with at least 3 years in a senior or lead capacity
- Strong expertise in Java and/or Kotlin — deep understanding of JVM internals and performance characteristics
- Hands-on experience with AWS services: EC2, ECS/EKS, RDS, SQS, Lambda, CloudWatch
- Experience designing and building distributed systems and event-driven architectures (Kafka, RabbitMQ)
- Understanding of RESTful API design principles and experience building internal and external APIs
- Strong understanding of SQL and experience with PostgreSQL or similar relational databases
- Familiarity with containerisation (Docker, Kubernetes) and modern CI/CD tooling
- Excellent communication skills — able to explain complex technical concepts to non-technical stakeholders
Desirable Skills
The following would be advantageous but are not essential:
- Experience in FinTech, payments processing or financial services
- Knowledge of PCI-DSS compliance requirements
- Experience with Kotlin Coroutines or reactive programming patterns
- Contributions to open source projects
- Experience with GraphQL or gRPC
- AWS certifications (Solutions Architect, Developer)
Technology Stack
Java 21
Kotlin
Spring Boot
AWS
Kubernetes
Docker
Kafka
PostgreSQL
Terraform
GraphQL
gRPC
Go
Benefits & Perks
- Competitive base salary of £75,000–£90,000 depending on experience
- Annual performance bonus of up to 15% of base salary
- EMI share option scheme — meaningful equity stake in the business
- 25 days annual leave plus bank holidays, with option to buy 5 more days
- Private medical insurance (BUPA) for you and your immediate family
- Enhanced pension: 6% employer contribution (standard) / 8% (matched)
- £3,000 annual learning & development budget for courses, conferences and certifications
- Monthly team socials, quarterly hackathons and annual off-site company retreat
- Top-spec MacBook Pro and home office setup allowance of £1,000
- Cycle to Work scheme and electric vehicle salary sacrifice programme