SELLKIT - Digital Product Marketplace Platform
Comprehensive marketplace platform allowing sellers to create their own stores, sell digital products, online courses with multi-gateway payment system and automated order management.
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Timeline
12 weeks
Team
3 people (PM, Frontend Developer, Backend Developer)
Client
Tech Startup
Budget
$1,600-2,400
About Project
SELLKIT is a complete marketplace platform built with microservices architecture, allowing sellers to create their own stores with custom subdomains, sell digital products (ebooks, templates, plugins, videos) and online courses. The system integrates multiple payment gateways (SePay, MoMo, COD), supports real-time notifications via WebSocket, manages files on AWS S3/R2, and provides detailed analytics dashboard for sellers. Backend built with NestJS following Clean Code standards, TypeScript strict mode, PostgreSQL with TypeORM. Frontend uses Next.js 15 with React 19, Tailwind CSS, Radix UI and Framer Motion.
Technologies Used
Key Features
Digital product management system with variants, pricing and file attachments
Online course system with curriculum, lessons, progress tracking and enrollment
Multi-gateway payment integration (SePay, MoMo, COD) with strategy pattern
Multi-subdomain architecture allowing each seller to have their own store
Real-time notifications via WebSocket and Server-Sent Events
Complete shopping cart and checkout flow with order management
Revenue analytics dashboard with detailed statistics and reports
Membership packages system with subscription management
File upload and management with AWS S3/R2, supporting image optimization
Blog/articles system with rich text editor (Tiptap)
Promotion system with discount codes and coupons
Admin panel with users, products, orders, payments management
Challenges
- •Building multi-subdomain architecture allowing each seller to have their own store with custom domain, requiring complex middleware for routing, cross-subdomain cookie sharing and authentication flow
- •Integrating multiple payment gateways (SePay, MoMo, COD) with different flows and webhooks, requiring abstraction layer for easy addition of new gateways and transaction state management
- •Building scalable real-time notifications system with thousands of concurrent users, requiring WebSocket connection optimization and message queuing implementation
Solutions
- •Using Next.js middleware to detect subdomain from hostname, dynamically rewrite URLs and set cookies with shared domain for cross-subdomain authentication token sharing
- •Applying Strategy Pattern with PaymentGatewayFactory to create abstraction layer for payment gateways, each gateway implements common interface with dependency injection in NestJS
- •Using Socket.IO with room-based architecture, each user joins their own room, combined with NestJS EventEmitter to emit events from business logic and Redis adapter for horizontal scaling
Results
- •Successfully built complete marketplace platform with 20+ modules, 100+ API endpoints
- •Multi-subdomain system allowing each seller to have their own store, increasing personalization and brand identity
- •Successfully integrated 3 payment gateways with flexible abstraction layer, easy to extend with new gateways
Client Testimonial
“SELLKIT helped us build a professional digital product selling platform with fast speed and excellent user experience.”
Founder SELLKIT
CEO & Founder
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