Voice Agent Booking Backend: Make.com Webhook Serving Live GHL Availability & Appointment Tools

Problem:

The voice agent could discuss appointments but had no live connection to the client's GoHighLevel calendar, it couldn't check real availability or actually book, forcing every call to end with 'someone will call you back.'

Solution:

Built a Make.com webhook backend that serves the agent's tool calls in real time. Inbound requests route into two branches: the availability branch searches GHL contacts, GETs calendar slots via HTTP, iterates and text-aggregates them through Tools, POSTs to /calendars/events/appointments, and returns structured webhook responses, with a Resume error handler keeping the agent alive when an API call fails mid-conversation. The lookup/booking branch searches GHL contacts, pulls records via HTTP, array-aggregates them, runs custom Make Code, parses the JSON, and routes to the correct webhook response or a follow-up HTTP POST. Every branch terminates in a webhook response so the agent receives an answer inside its tool-call timeout.

Result:

The voice agent now checks live calendar availability and books confirmed GHL appointments mid-call, converting 'we'll call you back' into a booked slot before hangup.