ZealSync — WiFi & Fiber ISP Billing Platform - Engineering Case Study

Tagline: Multi-tenant SaaS billing platform for Kenyan ISPs.

Problem: Small ISP operators in Kenya manage WiFi billing entirely by hand: reconciling M-Pesa SMS alerts against an Excel sheet, manually enabling PPPoE secrets and hotspot accounts in Winbox, and physically collecting cash from resellers. This consumes 3-4 hours per day per operator and causes revenue leakage, delayed activations, and reseller disputes.

Key Engineering Decisions

• UNIQUE constraint on mpesa_receipt_number enforces idempotency at the database layer, preventing double-provisioning under concurrent webhook delivery.
• arq background jobs (Redis-backed) decouple Daraja webhook acknowledgement from MikroTik provisioning — the webhook always returns 200 within the timeout window.
• WireGuard VPN tunnel keeps the MikroTik REST API completely off the public internet.
• Append-only wallet_transactions ledger with SELECT FOR UPDATE serialises concurrent reseller debits.

Case study by Fredrick Nyang'au — Backend Engineer based in Nairobi, Kenya, open to remote roles worldwide. Specialises in FastAPI, PostgreSQL, and M-Pesa Daraja integrations.