Plivo AI Agent not calling human agent after transferCall redirect

I have an inbound call flow where:

1. Incoming call → handled by /incoming, which connects the call to Ultravox AI through a .

2. AI Agent conversation → if the caller asks for a human, the AI triggers /transferCall/:fromNumber.

3. Transfer call → /transferCall returns Plivo XML with a to /agentDial.

4. Expected next step → Plivo should call /agentDial, which responds with to connect the human agent.

The issue is at step 3 → 4:

/transferCall runs and returns the as expected.

But Plivo never makes a request to /agentDial.

This means the call never dials out to the human agent, and it just gets stuck.

I’m unsure if the problem is with how I’m using (maybe I should return directly inside /transferCall?) or if I’m missing something in Plivo’s call flow setup.

What I tried

• I configured the AI Agent (Ultravox) to use the transferCall tool, which triggers my /transferCall/:fromNumber endpoint.

• In /transferCall, I return an XML pointing to /agentDial.

• I verified that /transferCall is definitely called (I see Received transferCall for ... in the logs).

• I expected Plivo to immediately make a POST to /agentDial, which would then run my logic to connect the caller to the human agent.

What I expected

• After /transferCall is triggered, Plivo should hit /agentDial.

• The /agentDial endpoint should respond with and connect the caller to the configured HUMAN_AGENT_NUMBER.

• The call should seamlessly transfer from the AI Agent to the human agent.

import express from "express";
import plivo from "plivo";

const app = express();

const PUBLIC_URL = process.env.PUBLIC_URL;
const PLIVO_NUMBER = process.env.PLIVO_NUMBER;
const HUMAN_AGENT_NUMBER = process.env.HUMAN_AGENT_NUMBER;

// Transfer Call
app.post("/transferCall/:fromNumber", (req, res) => {
    const fromNumber = req.params.fromNumber;
    console.log(`Received transferCall for ${fromNumber}`);

    res.type("text/xml").send(`<?xml version="1.0" encoding="UTF-8"?>
        <Response>
            <Redirect>${PUBLIC_URL}/agentDial</Redirect>
        </Response>`);
});

// Agent Dial
app.post("/agentDial", (req, res) => {
    console.log("🔥 *** AGENT DIAL ENDPOINT CALLED ***");
    try {
        const response = new plivo.Response();
        response.addSpeak("I will now transfer you to a human agent.");

        const dial = response.addDial({
            callerId: PLIVO_NUMBER,
            action: `${PUBLIC_URL}/dial-status`,
            method: "POST",
        });

        dial.addNumber(HUMAN_AGENT_NUMBER);
        res.type("text/xml").send(response.toXML());
    } catch (error) {
        console.error(error);
        res.type("text/xml").send(`
            <Response>
                <Speak>Could not connect to agent.</Speak>
            </Response>`);
    }
});

app.listen(3000, () => console.log("Server running on port 3000"));