How to Send WhatsApp OTP Automation in 2026

Why Switch from SMS to WhatsApp OTPs

Indian fintech, edtech, and ecommerce companies are migrating authentication flows from SMS to WhatsApp. Three reasons:

Add SMS fallback for the ~10% of users without WhatsApp and your overall delivery rate exceeds 99.5%.

What You'll Need

• A verified Meta Business Manager (required for Authentication templates).
• A WhatsApp Cloud API number. See our Cloud API setup guide if needed.
• A free PostEngage.ai account.
• Backend that can call HTTP APIs (any language: Node, Python, Go, Java, Ruby).
• Optional: SMS fallback provider (Plivo, Twilio, MSG91) for non-WhatsApp users.

Step-by-Step: WhatsApp OTP Setup

Step 1: Complete Meta business verification

Go to Business Settings > Security Center > Start Verification. Upload GST certificate or business registration. Approval in 2-5 days.

Step 2: Sign up for PostEngage.ai

Sign up at postengage.ai. Click Connect WhatsApp. Complete Meta embedded signup.

Step 3: Create an Authentication template

In PostEngage, go to Templates > New. Pick category Authentication. Use this template:

• Header: Verification Code
• Body: {{1}} is your verification code. For your security, do not share this code with anyone.
• Footer: This code expires in 5 minutes.
• Buttons: Copy Code (auto-fill button).

For Android autofill, add your app package name and SHA-256 cert hash to the button configuration.

Step 4: Submit the template to Meta

Click Submit. Authentication templates approve in 5-30 minutes — fastest of any category. You get an email when approved.

Step 5: Generate OTPs in your backend

Example Node.js:

function generateOtp() {
  return String(Math.floor(100000 + Math.random() * 900000));
}

async function sendOtp(phone) {
  const otp = generateOtp();
  await redis.set(`otp:${phone}`, otp, 'EX', 300);
  await sendWhatsAppOtp(phone, otp);
  return { ok: true };
}

Step 6: Call the PostEngage send-template endpoint

async function sendWhatsAppOtp(phone, otp) {
  const res = await fetch(
    'https://api.postengage.ai/v1/whatsapp/send-template',
    {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${process.env.POSTENGAGE_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        to: phone,
        template: 'verification_code',
        language: 'en',
        variables: [otp],
      }),
    }
  );
  return res.json();
}

Step 7: Set up Android autofill

Get your app's SHA-256 cert hash:

keytool -list -v -keystore ./release.keystore -alias mykey \
  | grep "SHA-256:" \
  | cut -d ' ' -f 3

Paste it into the template button. WhatsApp now tells your Android app the OTP directly — no manual typing.

Step 8: Add SMS fallback

Configure the PostEngage delivery webhook. If a WhatsApp send fails (status=failed within 10s), fall back to SMS via your provider. Use the same OTP value from Redis.

Step 9: Verify the OTP server-side

On user submission, fetch the stored OTP from Redis, compare, delete the key on success, return JWT or session token.

Step 10: Monitor metrics

PostEngage dashboard tracks: send rate, delivery rate, read rate, OTP success rate. Look for any single carrier showing abnormally low delivery — that signals a routing issue.

Common Issues and Fixes

Verify Delivery Performance

Three KPIs to watch in the PostEngage dashboard:

• 1. Delivery rate — target 98%+ on WhatsApp. Below 95% suggests a quality issue.
• 2. Median arrival time — target <3s. Spikes mean Meta is throttling.
• 3. OTP-to-success ratio — should be 85%+. Below means autofill is broken or copy is unclear.

The PostEngage Shortcut

PostEngage ships a pre-built "OTP Pack" — approved Authentication template, autofill config, SMS fallback webhook, and analytics dashboard:

Read more about free keyword auto-replies to add a HELP fallback so users can recover stuck flows.

FAQ