Notifications and secure transactions for v1 launch

The brief

Leatherback (Rexelpay) was launching a UK-based fintech platform — virtual accounts, onboarding, transactions, fund exchange — and needed someone to own the cross-cutting services that everything else depended on.

What I built

The notifications backbone

• Took ownership of the notifications microservice, written in C# and .NET Core. Used consumer / request-response strategies in MassTransit as a connector for RabbitMQ to communicate between services.
• Integrated Twilio-SendGrid for messaging capabilities across OTP, info exchange, and customer communications — boosting customer engagement by 35%.
• Became the project expert for the notifications service, handling inquiries and improvement suggestions across teams.

Secure transactions

• Designed and maintained transaction APIs alongside the digital banking team. Used Blowfish cipher (via bcrypt) for one-way hashing of transaction PINs.
• Applied Rijndael (AES) encryption for OTP and security-question two-way encryption.
• Designed APIs following SOLID principles with isolation of Presentation, Core, and Infrastructure layers, and CQRS for data flow isolation.

Pilot launch and security culture

• Led the pilot phase for v1 of the platform — virtual accounts, onboarding, transactions, and fund exchange — in close collaboration with the engineering team.
• Maintained extensive understanding of the OWASP Top 10, consistently identifying and mitigating web app security risks.
• Evaluated security implications of pull requests and architectural decisions during code reviews.