How to Build an AI Auto-Reply Viber Bot

Viber bots run on a Public Account and a simple REST API: you set a webhook, receive a JSON event for each message, and POST a reply. This guide creates the bot, registers the webhook, and wires incoming messages to an LLM so it answers automatically.

What you need

• A Viber account and a Public Account created at partners.viber.com
• The bot authentication token from the account info page
• A public HTTPS endpoint (Viber requires a valid certificate)
• Node 18+ and an AI API key

Step 1: Get your bot token

Sign in at partners.viber.com, create a bot account, and copy the token from the account info screen. Every API call carries this token in the X-Viber-Auth-Token header.

Step 2: Set the webhook

Tell Viber where to send events by calling set_webhook once. The event_types array controls which events you receive; message is the one you care about. Viber will reject any URL without a valid SSL certificate.

Step 3: Reply with AI

Each inbound message arrives as a POST with event: message. Read sender.id and message.text, generate an answer, and POST it back to send_message. Respond 200 quickly so Viber does not retry.

import "dotenv/config";
import express from "express";
import OpenAI from "openai";

const ai = new OpenAI();
const TOKEN = process.env.VIBER_TOKEN;
const app = express();
app.use(express.json());

app.post("/viber", async (req, res) => {
  res.sendStatus(200);
  if (req.body.event !== "message") return;

  const userId = req.body.sender.id;
  const text = req.body.message.text;

  const out = await ai.chat.completions.create({
    model: "gpt-5-mini",
    messages: [{ role: "user", content: text }],
  });

  await fetch("https://chatapi.viber.com/pa/send_message", {
    method: "POST",
    headers: {
      "X-Viber-Auth-Token": TOKEN,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      receiver: userId,
      type: "text",
      text: out.choices[0].message.content,
    }),
  });
});

app.listen(3000, () => console.log("Viber bot on :3000"));

Step 4: Subscribe and test

A user must say hi to your Public Account first; Viber then sends a conversation_started event and the user becomes a subscriber. After that, every message they send flows through your webhook.

Result

Your Viber Public Account now answers subscribers with AI. Deploy the server somewhere with a real certificate and Viber will keep delivering events without you touching the webhook again.