Full-Stack Developer to Convert B2B Automation Platform into SaaS

We have a working B2B automation platform currently used by one packaging-distribution company in Istanbul. We are looking for an experienced full-stack developer to help convert it into a secure, scalable multi-tenant SaaS product for distribution and wholesale companies. CURRENT PLATFORM - ERP/accounting integration with BizimHesap through REST APIs and n8n - Automated synchronization of customers, suppliers, products, inventory, statements, collections, and payables - WhatsApp bot for product and price inquiries, order handoff to sales staff, and task creation - B2B store built with Medusa v2, Next.js 15, and PostgreSQL - Management workflows for pricing, collections, suppliers, and overdue accounts - Telegram/Google Calendar assistant for reminders, meetings, and tasks - Docker Compose and Caddy deployment on Hetzner PROJECT OBJECTIVE Convert the existing single-company solution into a production-ready multi-tenant SaaS platform that can onboard new companies quickly and safely. EXPECTED SCOPE 1. Multi-tenant architecture - Design and implement strong tenant data isolation using separate schemas/databases or a well-secured tenant_id model - Define tenant-aware authorization, roles, permissions, and audit logs 2. Company onboarding - Create a repeatable onboarding flow for connecting a new company's ERP/accounting account and WhatsApp setup - Minimize developer intervention during onboarding 3. ERP adapter layer - Build a unified, replaceable integration layer - Support BizimHesap first, with a clear path for future systems such as Parasut and Logo - Handle REST APIs, webhooks, retries, logging, and synchronization failures 4. SaaS administration - Subscriptions and billing readiness - User and company management - Secure secrets/configuration management - Marketing-message consent and change history 5. Frontend and reporting - Build a proper standalone management dashboard instead of relying on n8n pages - Provide clear reports for collections, overdue receivables, supplier payables, inventory, and pricing - Support Arabic RTL as well as English; Turkish support is an advantage 6. Quality and operations - Automated tests, CI/CD, monitoring, backups, and staged deployments - Security and privacy review - Technical documentation and handover REQUIRED EXPERIENCE - Node.js and TypeScript - PostgreSQL and multi-tenant SaaS design - Next.js/React and data dashboards - REST APIs, webhooks, and ERP integrations - Docker, CI/CD, backups, monitoring, and application security STRONG ADVANTAGES - n8n automation - WhatsApp Business/Cloud API - LLM integrations - Medusa v2 - Arabic RTL applications - BizimHesap or Turkish accounting systems WORKING METHOD We prefer small, testable milestones. Each milestone must include documented delivery, automated tests where appropriate, and a clear acceptance checklist. Communication can be in English, Arabic, or Turkish. Existing code and documentation are in a private GitHub repository and will be shared only with the selected candidate. TECHNICAL SCREENING Shortlisted applicants will receive a small technical exercise: design a multi-tenant collections database schema covering companies, customers, invoices with due dates, and payments, then write a query that returns the overdue amount per customer while applying payments to the oldest invoice first. WHEN APPLYING, PLEASE INCLUDE - Two relevant multi-tenant SaaS or ERP-integration projects - Your exact role and the technologies used - A short outline of how you would approach tenant isolation and the ERP adapter layer - Your availability, hourly rate, and preferred communication language - Whether you can commit to documented milestone-based delivery