How to Send OTP Without DLT Registration — SMS API Docs

Overview

StartMessaging is a fully DLT-registered OTP provider. We have already completed entity registration, sender ID setup, and template approvals on the DLT platform.

When you send an OTP through our API, the message is routed through our pre-approved DLT channels. Telecom operators see a valid, registered message — so your OTPs get delivered just like any other DLT-compliant SMS.

This means you get full DLT compliance without any of the registration burden. No entity forms, no document uploads, no template approvals, no waiting.

Step-by-Step Guide

Step 1: Create Your Account

Step 2: Generate an API Key

Go to the API Keys page in your dashboard and click “Create API Key”. Copy the key — it is shown only once. The key starts with sm_live_ prefix.

Step 3: Top Up Your Wallet

Add funds to your wallet via Razorpay (UPI, cards, netbanking). Each OTP costs Rs 0.25.

Step 4: Send Your First OTP

Make a POST request to /otp/send with the phone number and OTP code inside the variables object.

curl -X POST https://api.startmessaging.com/otp/send \
  -H "Content-Type: application/json" \
  -H "X-API-Key: sm_live_your_api_key_here" \
  -d '{
    "phoneNumber": "+919876543210",
    "templateId": "YOUR_TEMPLATE_ID",
    "variables": {
      "otp": "123456",
      "appName": "YourApp"
    }
  }'

Step 5: Verify the OTP

When your user enters the OTP, call POST /otp/verify with the OTP request ID and the code. We handle validation, expiry, and attempt limits.

curl -X POST https://api.startmessaging.com/otp/verify \
  -H "Content-Type: application/json" \
  -H "X-API-Key: sm_live_your_api_key_here" \
  -d '{
    "requestId": "uuid-of-otp-request",
    "otpCode": "123456"
  }'

Frequently Asked Questions

DLT & Compliance FAQ

What is DLT registration?

DLT (Distributed Ledger Technology) is a framework mandated by TRAI (Telecom Regulatory Authority of India) for all commercial SMS senders in India. It requires businesses to register their entity, sender IDs, and message templates on a DLT platform before sending any SMS.

Is it legal to send OTPs without DLT registration?

Yes. StartMessaging is a registered entity on the DLT platform. When you use our API, your OTPs are sent through our pre-approved DLT-registered channels. You are essentially using our infrastructure, which is fully compliant.

Why is DLT registration difficult?

DLT registration involves multiple steps: entity registration with documents, sender ID (header) registration, and template approval for every unique message. The process takes 2-4 weeks, and any errors require resubmission.

How does StartMessaging handle DLT compliance?

We are registered on the DLT platform ourselves. When you send an OTP through our API, it goes through our pre-registered templates and sender IDs, so you do not need to do any DLT setup yourself.

Will my OTPs be delivered reliably without my own DLT registration?

Yes. Since we use our own DLT-registered templates, your OTPs are treated as legitimate transactional messages by telecom operators. We also use multi-provider failover to maximize delivery rates.

Can I customize the OTP message text?

Currently, OTPs are sent using our pre-approved templates optimized for delivery. The templates include your OTP code and are designed to be clear and professional.

General OTP API FAQ

Do I need any documents to sign up?

No. You can sign up with just an email address. No company registration, PAN card, GST certificate, or any other documents are required.

What phone number format should I use?

Use E.164 format: country code + number. For India, that is +91 followed by the 10-digit mobile number. Example: +919876543210.

How many OTPs can I send per second?

We support up to 20 OTPs per second globally per account. This ensures high throughput for production applications during peak times.

How long does an OTP remain valid?

OTPs expire after a configurable time window. The default expiry ensures security while giving users enough time to receive and enter the code.

What happens if SMS delivery fails?

StartMessaging automatically retries with a backup SMS provider. We only retry on service errors (5xx or timeout), not on validation errors like invalid phone numbers.