payments · backend · systems

Isaac Dwamena

Senior Software Engineer

I build the backend systems behind payments — Rails, Elixir, and USSD platforms that move money reliably across banking, microfinance, and telecom in emerging markets.

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About

Senior Software Engineer with 6+ years designing, building, and scaling enterprise FinTech platforms across banking, microfinance, and telecommunications. I specialise in Ruby on Rails backends, USSD payment systems, and Linux-based DevOps, with a track record of delivering merchant portals and payment applications that expand access to financial services — while enforcing regulatory compliance and mentoring engineering teams.

Experience
appsNmobile Solutions Ltd — Accra, Ghana

Senior Software Engineer

Feb 2023 – Present
  • Lead engineering across cross-functional teams delivering high-performance FinTech platforms — merchant portals and USSD payment systems serving thousands of users across banking, microfinance, and telecom.
  • Architect and scale Ruby on Rails management portals and USSD applications for reliability and throughput under production payment load.
  • Build and maintain CI/CD pipelines and Linux-based deployments (RedHat/CentOS, Nginx, Docker).
  • Integrate third-party banking and payment APIs while enforcing FinTech regulatory standards (AML, secure code review).
  • Mentor junior engineers and lead code reviews, raising code quality and delivery consistency across the team.
appsNmobile Solutions Ltd — Accra, Ghana

Junior Software Developer

Feb 2020 – Feb 2023
  • Developed and maintained features across Rails management portals and USSD applications supporting payment and financial workflows.
  • Integrated third-party APIs and built backend services, progressing to owning end-to-end delivery of platform modules.
  • Supported Linux-based deployments and production troubleshooting — earning promotion to Senior Software Engineer within three years.
Selected work
Flagship · built from scratch

Event Ticketing Platform

A three-service ticketing backend: a Ruby on Rails admin/back-office portal, an Elixir (Plug/Cowboy) transactional API, and a Ruby/Sinatra USSD channel for feature-phone customers — sharing a single PostgreSQL database and integrating with an external Mobile Money / SMS payment gateway.

  • Designed the service-to-service security model: IP-allowlisted internal endpoints for portal- and gateway-initiated operations, OTP-based purchase confirmation on the web channel, and telco-authenticated Mobile Money checkout on USSD with no separate PIN step.
  • Built asynchronous reconciliation workers (Elixir GenServers) to recover stuck payment transactions, retry undelivered SMS against real carrier delivery receipts, and apply scheduled ticket-price changes — reducing reliance on webhook delivery alone.
  • Built the full USSD purchase flow end-to-end: a Redis-backed session/menu state machine, in-session pagination for feature-phone screen limits, live ticket pricing, Mobile Money checkout, and QR ticket delivery via SMS.
  • Built the Rails admin portal — organizer onboarding, venue/show/ticket-type management, scanner assignment, role-based access control, and financial reporting/exports — with Devise + OTP authentication and Pundit authorization throughout.
ElixirPlug/CowboyRuby on Rails SinatraPostgreSQLRedis GenServer/OTPDevise + OTPPundit Mobile MoneyUSSD

Orchard Admin & Merchants Portal

Multi-tenant merchant management and payments portal built on Ruby on Rails.

Dalex Micro-Finance & Savings/Loans Portals

Lending and savings management platforms for a microfinance operation.

E-Ballot USSD & Portal

USSD-based balloting / voting platform with an administrative portal.

VPOS USSD & Management Portal

Virtual point-of-sale system — built and maintained end to end.

Skills
LanguagesRuby, Elixir, JavaScript, SQL
FrameworksRuby on Rails, Sinatra, ReactJS, FastAPI, Spring Boot
DevOps & InfraLinux (RedHat, CentOS), Nginx, Docker, Git, CI/CD, Shell
DatabasesPostgreSQL
ToolsRedis, FusionCharts, CKEditor, Cloudinary
DomainUSSD, API integration, system architecture, FinTech compliance (AML)
Certifications