Frixel Connect: 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.