The voice-AI lead machine,
explained end to end.

01System overview

One system handles leads in both directions. Outbound: the AI calls new leads in seconds and books them. Inbound: it answers every call 24/7 and books those too. n8n sits in the middle, orchestrating Retell, the GoHighLevel calendar, and the CRM.

The big picture

A new lead is created and tagged in GoHighLevel. Within seconds, n8n dials the lead with the AI agent. On the call it checks the calendar and books the appointment live, converting timezones and tagging the win. When the call ends, the system updates the CRM, moves the pipeline, and schedules the next touch in a 7-day / 7-call cadence, unless the lead asked to stop. Meanwhile, any inbound caller is answered 24/7, recognized as new or returning, and booked. Your team only shows up to the appointment, and every step is written back to the CRM.

The moving parts

Five layers do the work; n8n sits in the middle — it listens to GoHighLevel, makes the decisions, and orchestrates Retell, Twilio and the CRM.

The outbound dialer

Outcome A fresh lead is dialed by the AI within seconds, gated so bad numbers, already-booked, and after-hours leads are handled correctly, and call volume never exceeds Retell's concurrency limit.

n8n · UDT_Glendale_Make_Call — actual build

→ hands the live call to Calendar_BookingsOutbound · lead to booked call

Trigger

GoHighLevel pings the webhook the instant a lead is created or tagged. This is the speed-to-lead entry point for the whole outbound flow.

Module flow

1. intl_phone_gate—Validates the number. Bad or non-US numbers never get dialed. gate
2. Check Business Hours → Is Outside?—After hours, it generates a next-morning time and schedules the call instead of dialing at 2am. America/Phoenix
3. search_contact—Pulls the lead's full record from GoHighLevel.
4. self_book_gate—Already booked? Then don't call.
5. human_followup_gate—Flagged for a human? Then skip the bot.
6. Throttle_Batch / Throttle_Wait—Caps how many calls fire at once so it never blows past Retell's concurrency limit. concurrency
7. trigger_call—The POST to Retell that actually places the call. Retell

The real-time booking brain

Outcome While the agent is still on the call, it can see open times, book the appointment, reschedule, or read back what's booked. All against the real GoHighLevel calendar, timezone-correct.

n8n · UDT_Glendale_Calendar_Bookings — actual build

← used live by the call · booking tags drive Post_CallOutbound · lead to booked call

Trigger

The Retell agent calls these webhook functions live during the conversation, as tools it can reach for while talking.

Module flow

1. check_calendar_availability—"What's open Friday?" reads GHL free-slots and answers with real times.
2. book_appointment—"Book me Friday 2pm" converts the timezone, books in GHL, updates and tags the contact, then confirms. timezone tag
3. getOpenSlots—Returns human ranges ("Morning 9 to 12, Afternoon 1 to 5") and handles non-local callers.
4. reschedule (Get / Update Appointment)—"Move my appointment to next week" finds the event and updates it.
5. get appointment—"What do I have booked?" fetches the confirmed future appointment.

Mid-call memory

Outcome Whatever the AI learns on the call is written to GoHighLevel the moment it is said, so the record is current before the call even ends.

n8n · UDT_Glendale_Update_Contact — actual build

← called by the agent · writes to GoHighLevelOutbound · lead to booked call

Trigger

The Retell agent calls this webhook whenever it learns a fact worth storing.

Module flow

1. Webhook—The agent hits this with the field to save.
2. Update_GHL_Contact—Writes the value onto the contact in GoHighLevel. GHL
3. Respond—Confirms back to the agent so the call keeps flowing.

After every call

Outcome Every call ends with the CRM updated, the lead tagged, the pipeline moved, and the next touch already scheduled. A do-not-call request stops everything, for compliance.

n8n · UDT_Glendale_Post_Call — actual build

→ schedules the next call (7-day / 7-call cadence)Outbound · lead to booked call

Trigger

Retell calls this webhook the moment a call ends (the outbound agent's post-call webhook).

Module flow

1. dnc_check—First gate: if they said "stop calling," tag DNC and stop everything. compliance
2. Path · callback requested—Schedules a Retell call for their preferred time and updates GHL.
3. Path · not connected—Waits, checks for an existing appointment, then schedules the next call in the 7-day / 7-call cadence.
4. Path · connected, no booking—Updates GHL with everything the AI learned and schedules a same-day follow-up.
5. Write_Transcript_Note / Audit_Note—Writes the call summary back to the contact, so a human always sees what the bot did. visible artifact
6. update_pipeline_stage + tags—Moves the opportunity (New Lead → Contacted → Booked).

The 24/7 answering machine

Outcome Every inbound call is answered instantly. The AI knows your hours and whether the caller is new or returning, and either way they are in your CRM before the call ends. No missed calls, ever.

n8n · UDT_Glendale_InBound_call — actual build

→ returns caller context to the inbound agentInbound · 24/7 answering

Trigger

The Retell inbound agent fires this webhook the moment a call comes in.

Module flow

1. Config—Loads the GHL keys and location.
2. Check Business Hours → Set True/False → Merge—Passes open/closed status so the agent can say "we're closed now, but I can get you booked." America/Phoenix
3. Search_contact—Looks up the caller's phone number in GoHighLevel.
4. new_customer (If)—New caller → Create_Contact → respond. Returning caller → format their record → respond, and the agent greets them by name.

Booked-appointment Slack alert

Outcome Every booking pings the team's Slack channel with the appointment details. Instant visibility into what the AI is closing, without anyone watching the CRM.

n8n · UDT_Glendale_ApptBooked_Slack_Alert — actual build

fires on each new bookingOps & alerts

Trigger

Fires when an appointment is booked (the booking event).

Module flow

1. Trigger—Picks up the new booking.
2. Format message—Builds the alert: who, when, and which service.
3. Slack post—Drops the alert into the team channel. Slack

GoHighLevel · the CRM layer

GoHighLevel is the system of record: every lead, the pipeline, and the tags live here. A new lead tagged in GHL is the speed-to-lead trigger that fires the n8n outbound dialer, and every call writes its outcome straight back to the contact. UDT is voice-first, so GHL's job is to hold the lead and keep the record complete.

The tags that drive everything

Adding a tag in GoHighLevel is what fires an automation.

GHL-side workflows & pipeline

Retell · the voice agent

Retell is the voice. An outbound agent calls new leads in seconds and an inbound agent answers the line 24/7. Mid-call, the agent reaches into n8n through function tools to read and write the calendar in real time, the same booking brain documented above.

Functions — the tools the agent calls mid-call

Each is a live webhook into the n8n booking workflows. The agent must answer within Retell's ~10-second tool window, which is why the booking brain is built so tightly.

Dynamic variables — context passed in at call time

Injected from GoHighLevel so the agent knows the lead before it speaks:

Prompt structure

The agent prompt follows the engineer playbook, not improvisation. Its backbone:

Full workflow inventory

UDT voice-AI workflows with live status. firing = running now (Glendale) · standby = built, run on demand · off = inactive (other locations / paused). The six firing Glendale workflows are detailed in full above.

Glendale — live production firing

Other locations & on-demand

What triggers what

The master map: every source event, the workflow it hits, and what happens next.

Key IDs & config

Identifiers the Glendale workflows rely on. Secrets (keys/tokens) are redacted to their shape — real values live in the credential vault.

Who to contact