Senior Twilio Engineer — Two-Way Conversational SMS at Production Scale (Python / FastAPI)

Description Mutual NDA signed before any product detail or codebase is shared. The scope below describes the technical shape of the role only. We need a Twilio specialist to own a two-way conversational SMS channel for a B2C SaaS product. This is a conversational use case, not a marketing-blast or notification channel — inbound replies are the primary signal; deliverability, segment economics, and carrier compliance matter more than peak throughput. The bar is production discipline: every inbound message signature-validated, attributed to the right user, logged, and replied to within the webhook window. Scope of the role: Twilio Programmable SMS — inbound webhook handling (X-Twilio-Signature validation, fail-closed auth, sender resolution), outbound replies (TwiML synchronous + async REST send for longer turns) Phone-number provisioning, messaging service routing, sender-pool management 10DLC brand + campaign registration for conversational (not marketing) use cases Consent and opt-out handling (STOP/START/HELP), TCPA-aware capture and storage Long-running conversation context and message threading Segment economics and character-budget discipline Twilio Voice (Phase 2) — Programmable Voice + Media Streams Per-tenant cost attribution and carrier filtering diagnosis Required: Production Twilio with two-way conversational SMS — not outbound marketing Worked 10DLC brand + campaign registration end-to-end for a conversational use case Python + FastAPI webhook handlers (signature validation discipline is non-negotiable) Postgres for message logging and consent state Webhook security: signature validation, idempotency, replay protection TCPA / CTIA familiarity — knows where the traps are Nice to have: Twilio Conversations API, subaccounts Twilio Voice + Media Streams for agent-driven calling Carrier filtering diagnosis and remediation Worked on a product where SMS was the primary UX surface, not a notification channel How we work: 10–20 hrs/week, ongoing $90–150/hr depending on depth US time zone preferred Mutual NDA before any codebase or product detail Paid 4-hour trial against a sanitized webhook handler To apply: Line one: the largest two-way conversational SMS product you've shipped (not blast/marketing) and the trickiest carrier or compliance issue you personally debugged. Do not speculate about what we're building — describe what you've done. "I've used Twilio" gets archived. We need someone who treats SMS as a UI surface. Skills (mandatory) Twilio, Twilio API, SMS, Python, Webhook Skills (nice-to-have) Twilio Voice, FastAPI, PostgreSQL, TCPA Compliance, Telephony Settings Experience: Expert Type: Ongoing Hours: 10–20/week Duration: 3–6 months+ Location: U.S. only