GHL Systems Integration Engineer: Production-Grade Webhook/APIs

This is not a basic API connection or Zap project. We require strong experience with idempotent webhook systems, retry logic, Redis atomicity, and real-world integration debugging. Sports team ticket revenue accuracy and ledger integrity are mission-critical.
We are building a production-grade integration system between:
* TicketTailor (system of record for ticket sales)
* GoHighLevel (GHL) (CRM + automation engine)
* Vercel (serverless middleware)
* Upstash Redis (idempotency + ledger state)
This is not a basic API hookup.
* This is a correctness-first, revenue-sensitive webhook system with:
* HMAC validation
* Idempotent processing
* Retry handling
* Backfill migration logic
* CI-enforced test coverage
* Concurrency-safe ledger logic (phase 2)
ENGAGEMENT STRUCTURE
Commitment: 30–32 hours/week
Duration: 4–6 weeks
Start: ASAP
Timezone overlap: 3–4 hours overlap with US preferred
This is the sweet spot: enough weekly focus to main...