Integrate Twilio Inbound Calls with Vapi for HVAC Scheduling via Google Calendar API

TL;DR

Most HVAC shops lose 30% of inbound calls because they can't book appointments in real-time. This setup pipes Twilio inbound calls into a Vapi voice AI agent that extracts appointment details, checks Google Calendar availability, and auto-books slots—no human transfer needed. Stack: Twilio webhooks → Vapi function calling → Google Calendar API. Result: 24/7 scheduling, zero missed leads.

Prerequisites

API Keys & Credentials

Vapi API key (generate at dashboard.vapi.ai)

Twilio Account SID and Auth Token (from console.twilio.com)

Twilio phone number (inbound-capable, not trial)

Google Cloud project with Calendar API enabled

Google OAuth 2.0 credentials (service account or user credentials)

Software & Versions

Node.js 16+ (for webhook server)

npm or yarn package manager

ngrok or similar tunneling tool (for local webhook testing)

System Requirements

HTTPS-capable server (Twilio and Vapi require TLS for…