Voice AI Assistant Setup
Background and Purpose
This SOP outlines the setup of a voice-based AI agent capable of booking, rescheduling, and canceling appointments via phone calls. It walks through initial agent configuration, prompt setup, phone number setup, and calendar-based tool configuration. This process enables automated client interactions and appointment management for streamlined scheduling.
Step-by-Step Process
1. Voice Agent Initial Setup
Create New Agent: Go to Voice Agents and click Create Agent. Name the agent (e.g., "Katie") and choose whether it's an outbound or inbound agent.
Build the Prompt: VoicePalace agents run on Retell's LLM engine, so prompt writing follows Retell's own prompt engineering guidance for getting reliable, desired outcomes from the agent:
Use clear, concise, direct language — say exactly what the agent should do, without extra wording that adds length but not meaning.
Avoid patching every failure with a "do not" rule — if the agent keeps making the same mistake, revise the underlying instruction instead of stacking prohibitions on top of it.
Cover the happy path first, and only add edge-case handling once testing shows it's actually needed — don't write instructions for scenarios that haven't come up.
State each instruction once. Repeating the same guidance in multiple sections creates conflicts and maintenance headaches down the line.
Keep the whole prompt as short as it can be — a longer prompt gets reprocessed on every turn of the call, which slows the agent down and drives up cost.
Spell out tool calls explicitly — for each function the agent can use, the prompt needs the exact trigger (when to call it), required arguments, a boundary (when not to call it), and why. See Section 4 below for the specific tools this setup needs.
Structure the prompt around: Role (who the agent is and what it's for), a Call Flow Overview (the main steps in order), step-by-step instructions for each stage, and a closing section covering how the call ends and any special handling (holds, transfers, etc).
2. Telephony Setup
Select or Buy a Phone Number: Go to Phone Numbers and click Buy Phone Number to purchase a new Twilio number directly, or import an existing one.
Assign the Number to Your Agent: Open the number's details and set it as the Inbound call agent, Outbound call agent, or both — this is what connects a phone line to a specific agent so it can place or receive calls.
3. Configure Agent Tools
Add these three functions to the agent:
Check Appointment Availability — lets the agent view open slots before offering a time.
Schedule Appointment — books the appointment once the caller has agreed to a specific time.
End Call — closes out the call once booking is complete (or immediately, with no closing line, on silence, voicemail, or hostility).
Test each one on a real call and confirm the booking reflects correctly on the calendar.
4. Testing and Verification
Inbound Call Test: Call the agent directly and walk it through checking availability and booking. Confirm it reflects correctly on the calendar.
Outbound Call Test: Add a test lead, apply your trigger tag, and let the workflow fire the call. Review the call afterward in Calls — check the Transcription, Data, and Detail Logs tabs to confirm the conversation, variables, and tool calls all came through correctly.
5. Automation and Workflow Setup (Outbound Call)
In GHL, go to Automation and create (or edit) a workflow with a Contact Tag trigger.
Add the Start AI Voice Call action, select the Voice AI Agent, the From Phone Number, and map your Dynamic Variables.
Test the workflow against a real contact and confirm the outbound call fires and logs correctly.
FAQs
Can I use any phone number provider? Numbers are provisioned through the built-in Twilio integration directly in Phone Numbers — you don't need to bring your own SIP trunk.
How do I troubleshoot calls that aren't being logged? Check the GHL workflow — confirm the Start AI Voice Call action has the correct agent and phone number selected, then check the call's Detail Logs tab for errors.
Can I customize the agent's responses? Yes — edit the Style Guardrails and Response Guideline sections of the prompt, or rewrite the Script itself.