Transfer to Human Agent

When to hand an AI-handled call to a human agent, and how to choose between DID forward, SIP auth forward, and a Multiparty Call.

• What: Hand an AI-handled call to a human agent by phone, SIP, or Multiparty Call. Only a Multiparty Call does warm transfer.
• Watch out: A SIP transfer needs two Plivo IP ranges whitelisted, not one.

When your AI agent hits an escalation, a query it can’t handle, or a fallback, it hands the caller to a human agent. This page helps you pick how. Each option has its own page with the XML, API calls, and setup, and Troubleshooting covers failed transfers.

The video walks through all three options in about a minute. Select a chapter to jump to it.

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When to Transfer to a Human Agent

Transfer the caller to a human agent when your AI agent detects an escalation trigger, for example:

• The caller asks for a human.
• The caller’s intent is unclear.
• The query is one your AI agent can’t handle.
• Your AI agent hits a fallback.

A transfer is either cold or warm:

• Cold transfer: the caller is connected to the human agent, and your AI agent leaves the call without briefing them.
• Warm transfer: your AI agent briefs the human agent first, while the caller is on hold. Then the caller is connected.

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Transfer Approaches

Option	What It Does	Best For	Warm Transfer
Option 1: DID Forward	Transfer to a regular phone number	Simple call centers, agents on PSTN phones, no SIP infrastructure	No
Option 2: SIP Auth Forward (recommended)	Transfer to a SIP endpoint (softphone, contact center, PBX) with credentials	Modern contact centers, softphone-based agents, lower latency	No
Option 3: Multiparty Call	Put the caller, your AI agent, and the human agent in one Multiparty Call (MPC)	Warm transfer, and transfers that don’t wait for your AI agent’s WebSocket to close	Yes

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Choosing a Transfer Approach

Pick the option recommended for your situation:

• Your AI agent should brief the human agent before the caller joins (warm transfer): Option 3, Multiparty Call. Options 1 and 2 can’t do a warm transfer. Option 2 can still pass the call’s context in SIP headers.
• Your human agents answer on regular phone numbers: Option 1, DID forward.
• Your human agents use a SIP contact center, softphone, or PBX: Option 2, SIP auth forward.

Option 3 only works if your own server controls the call. It puts the caller in a Multiparty Call, then uses the Plivo API to add the human agent and remove the AI agent. If another platform answers calls on your Plivo number for you, use Option 1 or 2.

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Full API Reference

• Dial XML — Complete reference for <Dial>, <Number>, and <User> elements
• SIP Authentication — How outbound SIP auth works
• Voice Call API — Transfer a Call, to redirect a live call leg from your server
• Multiparty Call XML — <MultiPartyCall> and its participant roles, including ai-agent
• Multiparty Call API — Add, update, and kick participants
• Firewall and Network Configuration — Plivo IPs to whitelist
• Hangup Causes — Every hangup code and its meaning

Related

• Option 1: DID Forward — Transfer to a phone number

• Option 2: SIP Auth Forward — Transfer to a SIP endpoint with credentials

• Option 3: Multiparty Call — Cold or warm transfer in a Multiparty Call

• Troubleshoot Transfer to Human Agent — Test a transfer and fix failed ones

• Connect External Phone Numbers — Route external numbers into Plivo applications

• Build with Audio Streaming — AI voice agent setup

• SIP REFER — Transfers started by a platform connected over Plivo SIP Trunking, which work differently from the ones on this page