Hire the Best Fintech Software Engineers

I build payment systems and the AI agents that run on top of them. I am a senior backend engineer with 9+ years in Java and Spring Boot, including 4+ years on the billing and payments platform behind a marketplace moving about $4B a year. PAYMENTS AND FINTECH I deliver provider integrations end to end: Adyen, Braintree, Payoneer, PayPal, Venmo, Wise, Wells Fargo, Bank of America and Forter, on a platform operating across 180+ countries. My work covers card processing, wallets, payouts, bank transfers, fraud screening and reconciliation over REST, SFTP and webhooks. I have also integrated Stripe, FastSpring and bank vPOS in client products. Representative work: - Migrated a major payout provider from a legacy protocol to REST with OAuth 2.0. The migration covered payouts, mass payouts, payee registration, card release and reconciliation. I shipped it to 100% behind feature flags with no customer-facing incidents. I built provider emulators to test it without vendor sandboxes. - Designed a card-processing service on a provider's GraphQL API covering client tokens, payment methods, network tokens, cryptograms, authorization, capture, refunds, cancellations and 3D Secure. - Built a forwarding layer that routes network tokens between two providers, enabling non-US card acceptance. I rolled it out in stages and negotiated timeout SLAs directly with the vendor. - Authored the design for splitting a payments monolith into nine provider-specific microservices. Domain coverage: 3DS2, network tokenization, cryptograms, authorization and capture, refunds, chargebacks, reconciliation through APIs, webhooks and SFTP files, idempotency and double-charge prevention, mass payouts, ACH returns, fraud screening, PCI-aware design. AI AGENTS AND LLM SYSTEMS I build AI that runs inside products with real users and revenue. I built an agentic system that investigates failed payment transactions on its own, reasoning across logs, dashboards, source code and incident tooling to cut manual triage. I built it with Python, LangChain and multi-agent orchestration. It runs in a high-stakes payments environment, where being wrong has a cost. I also built and run Memabooks, a profitable AI commerce product that turns a child's photo into a personalized illustrated storybook. Over 10,000 books created so far, printed on demand and shipped worldwide, with customers in eight countries. I developed a multi-stage, identity-preserving image generation pipeline covering face detection, background removal, personalized character generation, skin-tone matching and character consistency across a complete book. I work with diffusion models, fine-tuned LoRA adapters and serverless GPU inference, tuning for quality, latency and cost. I also built the Node/NestJS backend, the Angular front end, print-on-demand fulfilment, and the payment stack for a market with limited access to major global processors: bank vPOS, 3DS2, Apple Pay, idempotency and double-charge prevention, and abandoned-payment recovery. AI stack: LangChain, LangGraph, LlamaIndex, multi-agent systems, RAG and multimodal RAG, vector databases (FAISS, Chroma), Model Context Protocol, OpenAI, Gemini, Azure AI. BACKEND ENGINEERING AND RANGE My core stack is Java 17 and Spring Boot. I also have production experience with Node.js, NestJS, TypeScript, Python, PostgreSQL, MongoDB, AWS, Docker, Kubernetes, REST, GraphQL, microservices and event-driven architecture. I was the sole engineer responsible for Geoapify's product surface for 17 months, working directly with the product owner across 14 repositories. I built a geocoding SaaS end to end, covering file upload, worker-based job processing, object storage and card payments. I maintained their public TypeScript SDKs for MapLibre GL, Leaflet and GeoJSON, which see about 55K npm downloads a month, and owned their public API playgrounds and OpenAPI specs. Testing is part of my delivery process. On one project, I built 260 Playwright end-to-end tests from scratch in about six days. WHAT I CAN HELP WITH - Payment provider and fintech integrations - Java and Spring Boot backend development - Backend architecture and monolith-to-microservices migrations - AI agents, RAG and LLM integration - API design, reliability, observability and production troubleshooting CREDENTIALS - Oracle Certified Professional: Java SE 11 Developer - IBM RAG and Agentic AI Professional Certificate - Google Cloud Generative AI Leader - Microsoft Azure AI Fundamentals - BSc in Computer Science, American University of Armenia - Former Java lecturer, Russian-Armenian University My longest engagement here ran 19 months and 2,700+ hours. I am open to long-term, full-time and contract-to-hire engagements. Tell me what you need built or what is currently breaking. I will tell you honestly whether I am the right engineer for it.

Hello, I am Oleksandr! 🔥I build AI-integrated SaaS and mobile apps for fintech, travel & hospitality, real estate and healthcare startups and established businesses. Using React Native, Python, and React, I deliver secure MVPs from concept to launch. Backed by a 65+ dev team, I ensure scalable, compliant solutions with predictable delivery and rapid iteration.🔥 🚀 I also lead a web development team, Join.To.IT from Kyiv, Ukraine, as co-founder and CEO. We have multiple Laravel developers (Senior PHP and Custom PHP MySQL), Python (Django), and JavaScript (React, Vue, React Native) developers. If your project needs a dedicated mobile app developer, we can staff that role quickly, while I stay involved as a full stack developer to keep architecture, delivery, and communication aligned. When the UI scope grows, a senior web developer can join the project while I remain the full stack developer responsible for end-to-end quality.🚀 I’m an experienced Laravel engineer, React engineer, Vue engineer, and React Native engineer with 14 years of production experience. As a full stack developer I can build backend APIs, admin panels, dashboards, and customer-facing apps, and as a web developer I pay attention to UI details that improve conversion and retention. I’ve completed a wide range of successful projects, from MVPs to large systems with long-term maintenance and continuous improvements. My skills: React React Native Software Architecture & Design Laravel Python Full-Stack Development API Development JavaScript PHP Web Application Development Node.js AWS Development MySQL Mobile App Development Django WordPress HTML5 Tailwind CSS Web Design API Integration Stack of technologies we use: ✅ HTML/CSS, Bootstrap, Tailwind ✅ JavaScript (React, Vue, Node.js, Express, AdonisJS, Nuxt) ✅ React Native for cross-platform mobile delivery ✅ API integrations (Stripe, PayPal, Twilio, TextMagic, Xero, DocuSign, Google Maps, Meta APIs, and more) ✅ API development (Laravel, Node/Express, Firebase, Python/Django, Go, REST, GraphQL) ✅ PWA (Progressive Web App) ✅ Databases: MySQL, PostgreSQL, MongoDB, DynamoDB, Elasticsearch ✅ Infrastructure: AWS, DigitalOcean, Firebase, Supabase ✅ DevOps and administration: LAMP, CentOS, Ubuntu As a full stack developer, I connect the front end, back end, and infrastructure so releases are smooth. When the scope includes native-like UX, I can collaborate with a mobile app developer without slowing down the API roadmap, and a web developer can refine UI flows while we keep the backend stable. You can hire me as a full stack developer for full ownership, or extend the team and keep me as the full stack developer leading architecture and delivery. If timelines are tight, add a mobile app developer to parallelize mobile features, and add a web developer to accelerate dashboards and front-end work. Our team has already worked in such industries as: ✅ Marketplace ✅ E-commerce ✅ Travel and Hospitality ✅ Custom ERP (Enterprise Resource Planning) ✅ ChatGPT integration (LLM model in your website front end) ✅ Automotive (car inspection, automotive ERP, car sharing, rental, selling) ✅ Social media (Tinder-like networks, short video platforms, communities) ✅ Sales (CRM systems for sales teams, retail, hospitals, sales departments) ✅ Sport (gym management systems, trainer platforms, fitness apps, club portals) ✅ Legal (document automation, AI-assisted legal processing) ✅ Healthcare (clinic management, booking, mental health software) ✅ Education (LMS, automated training, coaching marketplaces) ✅ Finance (fintech platforms, investment platforms, bank API integrations, calculators) ✅ Manufacturing (shop floor management and automation) ✅ Human resources (HRM systems) ✅ Digital marketing (Meta, Facebook/Instagram, TikTok, Google APIs, analytics) In our work history you’ll find successful products built with Laravel, PHP, JavaScript, MySQL, React, Vue, WordPress development, Web Development, Full Stack development and React Native, plus multiple systems built with Python (Django, Flask, FastAPI). I also use LLM capabilities and AI APIs (including OpenAI integrations) when they genuinely improve the product experience. We have 65 senior developers across PHP, JavaScript, MySQL, Python, Go, and Node.js. As a full stack developer, I can jump into an existing codebase, stabilize releases, fix bottlenecks, and plan the next iterations. Don't hesitate to get in touch with me for further details and fruitful work. Best regards, Oleksandr CEO, JoinToIT

Software Engineer | AI Engineer | Backend Architect Hi there! I’m a hard-working, results-oriented Software Engineer with deep experience in designing, building, and maintaining complex, high-impact systems. I thrive in environments that require sharp problem-solving, structured thinking, and relentless commitment to quality. With a Master’s degree in Artificial Intelligence and over 12 years of professional software engineering experience (since 2013), I have delivered solutions across banking & fintech, healthcare, blockchain, telecommunications, insurance, social media, and data analytics. I focus on understanding the WHY before implementing the HOW, ensuring every solution is scalable, maintainable, and aligned with business goals. In addition to software engineering, I also provide professional video editing services, creating engaging content for YouTube, social media, promotional videos, and educational content. I combine creativity with modern AI-powered workflows to deliver polished, visually appealing videos efficiently. ⸻ 🧩 Key Strengths • 🔹 Strong communication, leadership, and cross-team collaboration • 🔹 Solid theoretical background in AI, mathematics, and computer science • 🔹 Adaptable to evolving technologies, industries, and project requirements • 🔹 Results-driven mindset with a passion for clean architecture and scalable solutions • 🔹 Creative eye for storytelling, pacing, and visual content production ⸻ 🧠 Core Skills & Technologies 💻 Software Engineering Backend Engineering • Java 21 · Spring Boot · Spring Framework · Spring Security · Spring MVC · Spring Data JPA • Quarkus · Hibernate · RESTful APIs · JWT · JUnit · Cucumber · Reactive Programming · AML · Python for AI Frontend Engineering • Vaadin · Swing · JavaFX · Angular AI Integration & Engineering • Daily use of AI tools such as Claude Code for development acceleration • Reviewing, validating, and refining AI-generated outputs for quality and correctness • Context engineering and prompt engineering • AI-assisted software development and productivity optimization Cloud & DevOps • AWS (SES, SNS, S3, EC2, ELB, Lambda, Cognito, KMS, RDS, CloudWatch, Route53, IAM, API Gateway, CloudHSM, Rekognition, Secrets Manager, VPC) • Jenkins · GitHub Actions · GitLab CI · Maven · Gradle · SonarQube • Docker · Kubernetes (Basic) · ECS · EKS • Terraform (Learning) · CloudFormation (Basic) Architecture & System Design • Microservices · Event-Driven Architecture · DDD · REST APIs · Kafka · RabbitMQ · Redis · Apache Avro · Spring Cloud Databases • PostgreSQL · MySQL · MongoDB · Redis Testing & Quality • TDD · JUnit · Cucumber · RestAssured · Postman · SonarQube ⸻ 🎬 Video Editing • Professional editing for YouTube, Instagram, TikTok, Facebook, and promotional videos • Short-form and long-form content editing • Smooth cuts, transitions, pacing, and storytelling • Motion graphics, animated text, subtitles, and captions • Audio synchronization, cleanup, music, and sound effects • Color correction and basic color grading • AI-assisted editing workflows for faster, high-quality production ⸻ 🌍 Translation & Localization • Professional translation between English, French, Arabic, and Russian • Technical documentation and software localization • Business documents, contracts, certificates, and official correspondence • Proofreading, editing, and formatting • Accurate, culturally appropriate, and detail-oriented translations ⸻ 🚀 Professional Experience As a Software Engineer, I have worked on multiple enterprise systems: 1. Banking & FinTech: SEPA integration, online banking, high-load OLTP systems, blockchain (Hyperledger Fabric), KYC/KYB/AML, trading systems, performance optimization, architecture improvements, and business change requests. 2. Healthcare: High-security hospital and health insurance systems. 3. Blockchain: Smart contract integration and secure on-chain/off-chain solutions. 4. Social Media: Scalable backend services and REST APIs. 5. Telecommunications & MIS: Real-time event-driven systems using Kafka and microservices. 6. Analytics: Large-scale data aggregation and reporting pipelines. As a Video Editor, I create engaging visual content optimized for social media, educational platforms, and promotional campaigns, focusing on clean editing, storytelling, and audience engagement. ⸻ 🤝 Soft Skills • Strong team player and active listener • Self-motivated and results-oriented • Analytical problem solver with deep focus on complex systems • Fast learner with a passion for continuous improvement • Excellent communication and collaboration skills • Creative mindset with strong attention to detail.

🏆 𝐄𝐱𝐩𝐞𝐫𝐭-𝐕𝐞𝐭𝐭𝐞𝐝 - 𝗧𝗼𝗽 𝟭% 𝗼𝗻 𝗨𝗽𝘄𝗼𝗿𝗸 ✅ 𝟕+ 𝐘𝐞𝐚𝐫𝐬 𝐨𝐟 𝐄𝐱𝐩𝐞𝐫𝐢𝐞𝐧𝐜𝐞 ⏰ 𝟏𝟐𝟎𝟎𝟎 + 𝐔𝐩𝐰𝐨𝐫𝐤 𝐇𝐨𝐮𝐫𝐬 | 𝟏𝟎𝟎+ 𝐏𝐫𝐨𝐣𝐞𝐜𝐭𝐬 𝐃𝐞𝐥𝐢𝐯𝐞𝐫𝐞𝐝 ⭐️ $𝟕𝟎𝟎𝐤+ 𝐞𝐚𝐫𝐧𝐢𝐧𝐠 𝐨𝐧 𝐔𝐩𝐰𝐫𝐨𝐤 I’m Abdul, an Upwork Certified AI/LLM engineer with 7+ years of experience helping startups and growing teams build smart AI solutions. From autonomous agents, MVPs, AI-native products to intelligent analytics and cloud-ready deployments, I will help scale your operations, workflows, and revenue. —------------------------------------------------------------------- ⭐️𝐓𝐫𝐮𝐬𝐭𝐞𝐝 𝐛𝐲 𝐈𝐧𝐝𝐮𝐬𝐭𝐫𝐲 𝐋𝐞𝐚𝐝𝐞𝐫𝐬⭐️ “Abdul helped us rethink our lead gen with AI-powered decision-making. His work with LLMs and pipelines was key.” — HS, Director of Data & ML, EZ Pack “Game-changer. Abdul brought serious AI expertise that moved the needle fast.” — Thomas E., CEO, Mission BI —------------------------------------------------------------------- 𝐂𝐨𝐫𝐞 𝐒𝐞𝐫𝐯𝐢𝐜𝐞𝐬 & 𝐄𝐱𝐩𝐞𝐫𝐭𝐢𝐬𝐞 ➡️ 𝐆𝐞𝐧𝐞𝐫𝐚𝐭𝐢𝐯𝐞 𝐀𝐈 & 𝐂𝐨𝐧𝐯𝐞𝐫𝐬𝐚𝐭𝐢𝐨𝐧𝐚𝐥 𝐀𝐠𝐞𝐧𝐭𝐬 Autonomous LLM agents, domain-tuned business assistants, task automation, human-like conversational interfaces (OpenAI, Claude, open-source models) ➡️ 𝐑𝐀𝐆 (𝐑𝐞𝐭𝐫𝐢𝐞𝐯𝐚𝐥-𝐀𝐮𝐠𝐦𝐞𝐧𝐭𝐞𝐝 𝐆𝐞𝐧𝐞𝐫𝐚𝐭𝐢𝐨𝐧) Hybrid semantic search + generation, document & knowledge-base Q&A, contextual accuracy tuning, vector-store architecture ➡️ 𝐋𝐋𝐌 𝐅𝐢𝐧𝐞-𝐓𝐮𝐧𝐢𝐧𝐠 & 𝐄𝐯𝐚𝐥𝐮𝐚𝐭𝐢𝐨𝐧 Domain-specific fine-tuning (QLoRA), benchmark evaluation (perplexity, BLEU, custom QA metrics), reliability & guardrail testing ➡️ 𝐀𝐈 𝐀𝐮𝐭𝐨𝐦𝐚𝐭𝐢𝐨𝐧 Python-based workflow automation, process orchestration, manual-work reduction, API & systems integration, n8n, make. ➡️ 𝐀𝐈-𝐏𝐨𝐰𝐞𝐫𝐞𝐝 𝐀𝐧𝐚𝐥𝐲𝐭𝐢𝐜𝐬 Multi-agent data analysis, auto-generated dashboards & reports, structured + unstructured data pipelines, decision recommendations ➡️ 𝐂𝐥𝐨𝐮𝐝-𝐑𝐞𝐚𝐝𝐲 𝐃𝐞𝐩𝐥𝐨𝐲𝐦𝐞𝐧𝐭 Production-scale deployment on AWS (Bedrock, SageMaker), GCP (Vertex AI), Azure, and Databricks —------------------------------------------------------------------- 💰 𝐊𝐞𝐲 𝐀𝐜𝐡𝐢𝐞𝐯𝐞𝐦𝐞𝐧𝐭𝐬 -Helped clients raise $3M+ through AI-powered growth. -Built 50+ AI systems, from multi-agent tools to insight engines. -Drove a 17% revenue increase in 7 months for a US startup. -Impacted 300,000+ users through data-led product strategies. -Graduated in the Top 5% in my Master’s degree class (specialization in AI) —------------------------------------------------------------------- 🛠️ 𝐓𝐞𝐜𝐡 𝐒𝐭𝐚𝐜𝐤 LLMs & Agents: GPT-4, Claude, LLaMA, Mistral, LangChain, LlamaIndex, MemGPT RAG Stack: FAISS, ChromaDB, Pinecone, Weaviate LLM Ops: Fine-tuning, Prompt Engineering, Evaluation Metrics, Guardrails Dev & Infra: Python, FastAPI, LangGraph, Streamlit, Chainlit, Flask Data Pipelines: PySpark, SQL, Event-Driven Workflows, Cloud Functions Cloud Platforms: AWS, GCP, Azure, Bedrock, SageMaker, Vertex AI, Databricks —------------------------------------------------------------------- I am available to understand your project needs and deliver the best solution efficiently. Click on the “Message” button and let’s have a chat —------------------------------------------------------------------- Keywords associated with my skill set: AI Agent Developer, AI Consultant, Chatbot Developer, AI Automation Expert, AI Integration Specialist, Machine Learning Engineer, LLM Developer, Generative AI, Agentic AI, Multi-Agent Systems, Large Language Models (LLMs), GPT-4, Claude, LLaMA, Mistral, LangChain, LlamaIndex, LangGraph, Retrieval-Augmented Generation (RAG), Semantic Search, Knowledge Retrieval, Vector Databases, FAISS, ChromaDB, Pinecone, Weaviate, Custom Embeddings, Memory Layers, Prompt Engineering, LLM Fine-Tuning, LLM Evaluation, MLOps, Model Deployment, AI Data Analysis, NLP, Python, FastAPI, Chainlit, Data Pipelines, PySpark, SQL, AWS, GCP, Azure, Bedrock, Vertex AI, SageMaker, Databricks, Cloud Functions, API Integration, Open Source Models, Healthcare AI Engineer, Healthtech, Edutech, Fintech.

Quality Assurance is more than finding bugs; it's about building reliable products, reducing release risks, and delivering exceptional user experiences. With 30,000+ hours of hands-on Software Quality Assurance experience, I've helped Startups, SaaS companies, enterprises, and AI product teams deliver stable, scalable, and production-ready applications through Manual Testing, Automation Testing, API Testing, AI Testing, and End-to-End Quality Assurance. Over the years, I've tested a wide range of products, including web applications, mobile applications (iOS & Android), desktop software, enterprise solutions, AI-powered platforms, APIs, and cloud-based SaaS products. My goal is simple: identify issues before your users do and help your team release with confidence. Recently, I've been actively involved in testing AI-powered products, including conversational AI, AI chatbots, AI agents, and LLM-based applications. My work includes validating AI workflows, prompt behavior, response quality, integrations, edge cases, and real-world user scenarios to improve reliability, consistency, and overall user experience. 🚀 Services I Provide • Manual Testing • Automation Testing • API Testing • AI Product Testing & Validation • Web Application Testing • Mobile App Testing (iOS & Android) • Functional Testing • Regression Testing • End-to-End Testing • Integration Testing • Exploratory Testing • Smoke & Sanity Testing • User Acceptance Testing (UAT) • Cross-Browser & Cross-Platform Testing • UI/UX & Usability Testing • Payment Gateway & Subscription Flow Testing 🧠 AI Testing & Validation • AI Chatbot Testing • AI Agent Testing • Conversational AI Testing • LLM Testing & Validation • Prompt & Response Validation • AI Workflow Testing • AI Integration Testing • Voice AI Testing • AI Feature Validation • Context Retention & Session Testing • Hallucination & Edge Case Validation • Human-in-the-Loop Testing 🤖 Automation Testing • Playwright • Selenium WebDriver • Cypress • Appium • TestNG • Cucumber (BDD) • Maven • Automation Framework Development & Maintenance • Automated Regression & Smoke Testing • CI/CD Integration (Jenkins, GitHub Actions, GitLab CI/CD, CircleCI, Bitbucket Pipelines) 🔗 API Testing • REST API Testing • Postman • Swagger / OpenAPI • Request & Response Validation • Authentication & Authorization Testing • API Integration Testing • API Regression Testing • JSON Validation 💻 Programming Languages • Java • JavaScript • TypeScript • Python • Ruby 🛠 QA Tools & Platforms • Jira • Azure DevOps • TestRail • Zephyr • BrowserStack • Sauce Labs • Postman • Swagger • GitHub • GitLab • Bitbucket • Trello • Asana • ClickUp • Linear • Slack • Notion 🏢 Industry Experience • SaaS Applications • AI & Generative AI Products • FinTech • Healthcare • E-commerce • ERP / CRM / HRMS • WordPress & CMS Platforms • Real Estate • Enterprise Applications • Social Networking Platforms 📋 QA Deliverables • Test Strategy & Test Planning • Test Cases & Test Scenarios • Test Execution & Release Validation • Bug Reporting & Defect Management • API Test Documentation • Test Summary Reports • Regression Test Suites • QA Documentation & Release Sign-off Support ⭐ Why Clients Choose Me ✔ 30,000+ Hours of Professional QA Experience ✔ Top Rated Plus Freelancer with Proven Delivery Record ✔ Expertise in Manual, Automation, API & AI Testing ✔ Strong Focus on Product Quality & Release Readiness ✔ Clear, Reproducible & Developer-Friendly Bug Reports ✔ Experience Working with Agile Development Teams ✔ Flexible Communication & Time Zone Overlap Whether you're launching a new product, improving an existing application, building an automation framework, validating APIs, or testing AI-powered features, I can help ensure your software is reliable, scalable, and ready for production. Let's connect and discuss how I can help improve the quality of your next release. 🔑 Core Skills & Keywords Software Quality Assurance, Software Testing, Manual Testing, Manual QA, Automation Testing, QA Automation, Selenium, Playwright, Cypress, Appium, API Testing, REST API Testing, Postman, Swagger, Functional Testing, Regression Testing, Integration Testing, End-to-End Testing, Exploratory Testing, Smoke Testing, Sanity Testing, Cross-Browser Testing, Cross-Platform Testing, Mobile App Testing, Web Application Testing, AI Testing, AI QA, AI Product Testing, AI Chatbot Testing, AI Agent Testing, LLM Testing, Prompt Validation, Conversational AI Testing, Voice AI Testing, SaaS Testing, QA Engineer, Software Tester, Quality Assurance.

25 years in fintech and banking — the last 5 deep in production AI. From Oracle and IBM enterprise systems to hands-on CTO and Lead Engineer of a live EU payments platform, to production AI in regulated environments. I don't build demos. I build systems that run under load, with real financial consequences. Recent production builds: → RAG platform processing 1M documents (ColPali + BGE) - 5 enterprise deals → Fraud detection ML for Raiffeisen Bank Austria - 70% loss reduction, 100k txns/month → Fine-tuned LLM Knowledge Assistant - deployed to 5 enterprises Fintech AI: fraud detection · KYC/AML · credit scoring · open banking · PSD2 · Stripe/Plaid AI systems: RAG pipelines · LLM agents · HITL workflows · computer vision (YOLO, VLMs) Stack: Python · PyTorch · LangChain/LangGraph · FastAPI · React/Next.js · CISSP certified Available for production AI and fintech engagements. EU-based, immediate start.