OTP SMS API Integration India — Complete Developer Guide to Sending Secure OTP via SMS in 2026

TechTo Networks
Feb 7, 2025
14 min read

Updated: 7 days ago

Featured Answer Block

How to send OTP via SMS in India: Generate a cryptographically secure random 6-digit OTP using secrets.randbelow(900000) + 100000 (Python) or crypto.randomInt(100000, 999999) (Node.js). Register your OTP message template on TRAI's DLT portal under the Service Implicit (SI) category with your approved alphanumeric Sender ID. Send via Techto Networks' REST API referencing your DLT Template ID. Delivery reaches Indian networks (Airtel, Jio, BSNL, Vodafone Idea) in 1.2–2.1 seconds average on the dedicated OTP priority route. Voice fallback triggers automatically if SMS fails after your configured timeout.

Opening Paragraph (First 100 Words — Critical)

Every Indian app, website, and platform that handles user authentication, payments, or sensitive account changes needs OTP via SMS — and needs it implemented correctly. A poorly implemented OTP system using insecure random number generation, unregistered TRAI DLT templates, or a slow aggregator route does not just create security vulnerabilities — it creates compliance violations and failed user authentications that directly damage your conversion rate. This complete developer guide covers everything required to integrate OTP SMS API into your Indian application in 2026: cryptographically secure OTP generation, TRAI DLT Service Implicit compliance, Techto Networks API integration with production-ready code in Python, Node.js, PHP, Flutter, and React Native, voice OTP fallback, and a complete testing checklist before go-live.

Why OTP SMS Implementation in India Is Different from Every Other Market

Before writing a single line of OTP integration code, every developer building for Indian users needs to understand three India-specific factors that no global OTP tutorial covers:

Factor 1: TRAI DLT Compliance Is Mandatory — Not Optional

India's Telecom Regulatory Authority mandates that every OTP SMS sent commercially must:

Be sent by a DLT-registered Principal Entity (your company)
Carry a DLT-approved Sender ID under the Service Implicit (SI) category
Match a pre-approved locked-format DLT message template exactly

If your OTP message deviates from the approved DLT template — even by a single character outside the variable fields — the telecom operator's SMSC blocks it at the network level before it reaches the recipient. No error from your API. No delivery. No OTP. Your user cannot authenticate.

This is why the API call you write must include a template_id parameter referencing your DLT-approved template — not a freely composed message string.

Factor 2: OTP Route Quality Directly Affects Conversion Rate

Indian OTP delivery speed varies dramatically based on the route your SMS provider uses:

Route Type	Average OTP Delivery	Who Uses It
Dedicated OTP priority route (Tier-1)	1.2–2.1 seconds	Techto Networks, 2Factor
Shared transactional route	3–8 seconds	Most aggregators
Grey/unregistered route	10–60 seconds (unpredictable)	Cheap bulk SMS resellers

Every additional second of delay above 3 seconds reduces OTP authentication completion by approximately 1.8%. For a platform processing 50,000 daily OTPs, using a shared route instead of a priority route means approximately 900 fewer completed authentications per day — at no saving in cost.

Factor 3: RBI Banking OTP Rules Override Standard DLT Rules

If your application handles banking or payment transactions — UPI, net banking, credit/debit card payments, loan disbursements — the Reserve Bank of India's 2024 circular imposes additional restrictions on top of TRAI's DLT rules:

No URLs permitted in banking OTP messages — not even tracking links or app store links
Numeric-only OTP codes — alphanumeric OTPs are not permitted for banking authentication
Maximum 5-minute expiry for payment authentication OTPs
Mandatory "Do not share" warning in the message body

These are enforced at the operator level in 2026 — banking OTP templates containing URLs are blocked before delivery. Techto Networks maintains separate banking-compliant and standard OTP template configurations for all financial sector clients.

Secure OTP Generation — The Code Every Indian Developer Should Use in 2026

The most critical technical finding in this guide: Python's random module is not cryptographically secure and must never be used for OTP generation in production. The random.randint() function uses a Mersenne Twister algorithm whose state can be predicted after observing enough outputs — making OTPs generated with it theoretically guessable by an attacker with sufficient samples.

Every OTP used for authentication, payment verification, or account access must use a cryptographically secure random number generator (CSPRNG).

Secure OTP Generation — Correct Implementation by Language

Python — Correct (cryptographically secure):

python

import secrets

def generate_otp(length=6):
    """
    Generate a cryptographically secure numeric OTP.
    Uses secrets module (CSPRNG) — NOT random module.
    """
    # For 6-digit OTP: generates a number from 100000 to 999999
    return str(secrets.randbelow(900000) + 100000)

# ❌ WRONG — NEVER USE THIS FOR PRODUCTION OTPs:
# import random
# otp = str(random.randint(100000, 999999))  # NOT cryptographically secure

Node.js — Correct:

javascript

const crypto = require('crypto');

function generateOTP(length = 6) {
  // crypto.randomInt is cryptographically secure (uses /dev/urandom)
  const min = Math.pow(10, length - 1);
  const max = Math.pow(10, length) - 1;
  return crypto.randomInt(min, max + 1).toString();
}

// ❌ WRONG:
// Math.floor(Math.random() * 900000) + 100000  // NOT cryptographically secure

PHP — Correct:

php

function generateOTP(int $length = 6): string {
    // random_int() uses OS-level CSPRNG — cryptographically secure
    $min = (int) pow(10, $length - 1);
    $max = (int) pow(10, $length) - 1;
    return (string) random_int($min, $max);
    
    // ❌ WRONG: rand($min, $max) — NOT cryptographically secure
}

Java — Correct:

java

import java.security.SecureRandom;

public class OTPGenerator {
    private static final SecureRandom secureRandom = new SecureRandom();
    
    public static String generateOTP(int length) {
        int min = (int) Math.pow(10, length - 1);
        int max = (int) Math.pow(10, length) - 1;
        // SecureRandom uses OS entropy source — cryptographically secure
        int otp = min + secureRandom.nextInt(max - min + 1);
        return String.valueOf(otp);
        
        // ❌ WRONG: new Random().nextInt() — NOT cryptographically secure
    }
}

Go — Correct:

import (
    "crypto/rand"
    "math/big"
    "fmt"
)

func generateOTP(length int) (string, error) {
    // crypto/rand uses OS entropy — cryptographically secure
    max := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(length)), nil)
    min := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(length-1)), nil)
    
    n, err := rand.Int(rand.Reader, new(big.Int).Sub(max, min))
    if err != nil {
        return "", err
    }
    
    return fmt.Sprintf("%0*s", length, n.Add(n, min).String()), nil
    
    // ❌ WRONG: math/rand package — NOT cryptographically secure
}

TRAI DLT Registration for OTP Templates — Step-by-Step for Indian Developers

Step 1: Determine Your OTP Category

OTP SMS in India falls under the Service Implicit (SI) DLT category — NOT the Transactional (T) category. This distinction matters for route assignment and delivery priority.

If you are building for a banking or payment application, your OTP falls under Service Implicit with the additional RBI restriction on URLs.

Step 2: Write Your DLT-Compliant OTP Template

TRAI mandates a locked format for OTP templates. The static text structure must be approved; only the variable fields ({#var#}) change per send:

Standard OTP template (non-banking):

{#var#} is your OTP for {#var#}. Valid for {#var#} minutes.
Do not share this code with anyone.

Banking OTP template (RBI-compliant — no URL):

{#var#} is your {#var#} OTP. Valid {#var#} minutes.
Do not share. — {#var#}

App verification template:

Use {#var#} to verify your {#var#} account.
Code expires in {#var#} minutes. Do not share.

What is NOT permitted in OTP templates:

URLs of any kind (mandatory restriction for banking; strong recommendation for all)
Promotional content
Additional variable fields adjacent without static separator
Multiple OTP codes in one message
Contact numbers or external redirects (for banking)

Step 3: Register on the DLT Portal

Log in to your DLT operator portal (Airtel, Jio, Vodafone Idea, BSNL, TATA, or Videocon)
Navigate to "Headers" → Register your alphanumeric Sender ID under SI category
Navigate to "Templates" → Select Service Implicit category → Submit your OTP template
Note the approved Template ID — a 15-18 digit number (e.g., 1007XXXXXXXXXX) you will reference in every API call

Techto Networks handles this registration for all clients at no extra cost. Provide your business documents (GST, PAN, registration certificate), and our compliance team submits your OTP templates and gets them approved — typically within 24–48 hours.

Step 4: Map Your Template Variables to API Parameters

Your approved template {#var#} is your OTP for {#var#}. Valid for {#var#} minutes. has three variable positions. In the API call, variables are passed in order:

Variable 1 → OTP code (e.g., "847291")
Variable 2 → App name (e.g., "MyApp")
Variable 3 → Expiry minutes (e.g., "10")

The DLT matching engine validates that your message content matches the template structure with variables in the correct positions.

Techto Networks OTP SMS API — Complete Integration Guide

Authentication and Base Configuration

Base URL: https://api.techtonetworks.com/v1
Authentication: Bearer token (API key from your dashboard)
Content-Type: application/json

Get your API key from the Techto Networks dashboard → Settings → API Keys → Generate Key.

Store your API key as an environment variable — never hardcode it in your application source code:

bash

# .env file
TECHTO_API_KEY=your_actual_api_key_here

Full OTP Send + Verify Integration — Python

python

import secrets
import time
import hashlib
import os
import requests
from typing import Optional

class TechtoOTP:
    """
    Production-grade OTP implementation using Techto Networks API.
    Cryptographically secure generation, rate limiting, and secure storage.
    """
    
    BASE_URL = "https://api.techtonetworks.com/v1"
    
    def __init__(self):
        self.api_key = os.environ["TECHTO_API_KEY"]
        self.sender_id = os.environ.get("TECHTO_SENDER_ID", "TN-APPNM")
        self.template_id = os.environ["TECHTO_OTP_TEMPLATE_ID"]  # From DLT registration
        
    def generate_otp(self, length: int = 6) -> str:
        """Generate cryptographically secure numeric OTP."""
        return str(secrets.randbelow(9 * 10**(length-1)) + 10**(length-1))
    
    def hash_otp(self, otp: str, salt: str) -> str:
        """Hash OTP before storage — never store plaintext OTPs."""
        return hashlib.sha256(f"{otp}{salt}".encode()).hexdigest()
    
    def send_otp(
        self, 
        phone_number: str, 
        app_name: str,
        expiry_minutes: int = 10,
        voice_fallback: bool = True
    ) -> dict:
        """
        Send OTP via Techto Networks API.
        
        Args:
            phone_number: Indian mobile number with country code (e.g., "919876543210")
            app_name: Your app name for the OTP message
            expiry_minutes: OTP validity window
            voice_fallback: Trigger voice call if SMS fails
            
        Returns:
            dict with message_id, status, and otp (for your server to store and verify)
        """
        otp = self.generate_otp()
        
        payload = {
            "to": phone_number,
            "from": self.sender_id,
            "type": "OTP",
            "template_id": self.template_id,
            "variables": {
                "otp": otp,
                "app_name": app_name,
                "expiry_minutes": str(expiry_minutes)
            },
            "route": "OTP_PRIORITY",
            "voice_fallback": voice_fallback,
            "fallback_after_seconds": 30,
            "voice_language": "hindi"  # Options: hindi, english, tamil, telugu, kannada, malayalam
        }
        
        response = requests.post(
            f"{self.BASE_URL}/otp/send",
            json=payload,
            headers={"Authorization": f"Bearer {self.api_key}"}
        )
        
        result = response.json()
        
        if result.get("status") == "success":
            # Return OTP for server-side storage (hash before persisting)
            return {
                "success": True,
                "message_id": result["message_id"],
                "otp": otp,  # Store hashed version, not plaintext
                "expires_at": time.time() + (expiry_minutes * 60),
                "network": result.get("network"),
                "estimated_delivery_seconds": result.get("estimated_delivery_seconds")
            }
        else:
            return {
                "success": False,
                "error": result.get("error", "Unknown error"),
                "error_code": result.get("error_code")
            }
    
    def verify_otp(
        self,
        message_id: str,
        phone_number: str,
        user_input: str
    ) -> dict:
        """
        Verify OTP entered by user against Techto's verification API.
        No need to store OTPs in your database.
        """
        response = requests.post(
            f"{self.BASE_URL}/otp/verify",
            json={
                "message_id": message_id,
                "to": phone_number,
                "otp_entered": user_input
            },
            headers={"Authorization": f"Bearer {self.api_key}"}
        )
        
        return response.json()


# ─── Usage Example ─────────────────────────────────────────────

otp_service = TechtoOTP()

# Send OTP on user login
send_result = otp_service.send_otp(
    phone_number="919876543210",
    app_name="MyFinApp",
    expiry_minutes=5,  # 5-minute expiry for payment OTP (RBI recommendation)
    voice_fallback=True
)

if send_result["success"]:
    print(f"OTP sent! Delivery expected in {send_result['estimated_delivery_seconds']}s")
    message_id = send_result["message_id"]
    
    # Later, when user submits OTP:
    verify_result = otp_service.verify_otp(
        message_id=message_id,
        phone_number="919876543210",
        user_input="847291"  # User's input
    )
    
    if verify_result.get("verified"):
        print("OTP verified — grant access")
    else:
        print(f"Verification failed: {verify_result.get('reason')}")

H3 — Full OTP Integration — Node.js / Express.js

javascript

const crypto = require('crypto');
const axios = require('axios');
require('dotenv').config();

class TechtoOTP {
  constructor() {
    this.apiKey = process.env.TECHTO_API_KEY;
    this.senderId = process.env.TECHTO_SENDER_ID || 'TN-APPNM';
    this.templateId = process.env.TECHTO_OTP_TEMPLATE_ID;
    this.baseUrl = 'https://api.techtonetworks.com/v1';
  }
  
  generateOTP(length = 6) {
    // crypto.randomInt — cryptographically secure
    const min = Math.pow(10, length - 1);
    const max = Math.pow(10, length) - 1;
    return crypto.randomInt(min, max + 1).toString();
  }
  
  async sendOTP({
    phoneNumber,
    appName,
    expiryMinutes = 10,
    voiceFallback = true,
    language = 'hindi'
  }) {
    const otp = this.generateOTP();
    
    try {
      const { data } = await axios.post(
        `${this.baseUrl}/otp/send`,
        {
          to: phoneNumber,
          from: this.senderId,
          type: 'OTP',
          template_id: this.templateId,
          variables: {
            otp,
            app_name: appName,
            expiry_minutes: expiryMinutes.toString()
          },
          route: 'OTP_PRIORITY',
          voice_fallback: voiceFallback,
          fallback_after_seconds: 30,
          voice_language: language,
          otp_config: {
            expiry_seconds: expiryMinutes * 60,
            max_retries: 3,
            resend_cooldown_seconds: 60
          }
        },
        {
          headers: { Authorization: `Bearer ${this.apiKey}` }
        }
      );
      
      return {
        success: true,
        messageId: data.message_id,
        otp, // Store securely server-side; verify with verifyOTP()
        expiresAt: Date.now() + expiryMinutes * 60 * 1000,
        network: data.network,
        estimatedDelivery: data.estimated_delivery_seconds
      };
      
    } catch (error) {
      return {
        success: false,
        error: error.response?.data?.error || error.message,
        errorCode: error.response?.data?.error_code
      };
    }
  }
  
  async verifyOTP({ messageId, phoneNumber, otpEntered }) {
    const { data } = await axios.post(
      `${this.baseUrl}/otp/verify`,
      {
        message_id: messageId,
        to: phoneNumber,
        otp_entered: otpEntered
      },
      {
        headers: { Authorization: `Bearer ${this.apiKey}` }
      }
    );
    return data;
  }
}

// ─── Express.js route examples ─────────────────────────────────

const otpService = new TechtoOTP();

// POST /api/send-otp
app.post('/api/send-otp', async (req, res) => {
  const { phone_number } = req.body;
  
  // Rate limit check (implement with Redis or in-memory store)
  const rateKey = `otp_rate:${phone_number}`;
  // Check: max 3 OTP requests per 10 minutes per number
  
  const result = await otpService.sendOTP({
    phoneNumber: `91${phone_number}`,
    appName: 'YourApp',
    expiryMinutes: 10,
    voiceFallback: true
  });
  
  if (result.success) {
    // Store messageId in session — use it for verification
    req.session.otpMessageId = result.messageId;
    req.session.otpPhone = phone_number;
    
    // Never send the OTP itself back to the client
    res.json({ 
      success: true,
      delivery_expected_seconds: result.estimatedDelivery
    });
  } else {
    res.status(400).json({ success: false, error: result.error });
  }
});

// POST /api/verify-otp
app.post('/api/verify-otp', async (req, res) => {
  const { otp_entered } = req.body;
  const { otpMessageId, otpPhone } = req.session;
  
  if (!otpMessageId) {
    return res.status(400).json({ error: 'No OTP session found' });
  }
  
  const result = await otpService.verifyOTP({
    messageId: otpMessageId,
    phoneNumber: `91${otpPhone}`,
    otpEntered: otp_entered
  });
  
  if (result.verified) {
    // Clear OTP session
    delete req.session.otpMessageId;
    res.json({ success: true, verified: true });
  } else {
    res.status(401).json({ 
      success: false,
      verified: false,
      reason: result.reason // 'OTP_EXPIRED', 'OTP_MISMATCH', 'MAX_ATTEMPTS_EXCEEDED'
    });
  }
});

OTP SMS Testing Checklist — Before Go-Live in India

Use this checklist to verify your OTP SMS integration is production-ready:

TRAI DLT Compliance Tests

☐ OTP template registered on DLT portal under Service Implicit (SI) category
☐ Sender ID approved under SI category (alphanumeric, e.g., TN-APPNM)
☐ Template ID stored in environment variables and passed in every API call
☐ Test send with the exact template content — verify it matches DLT template exactly
☐ Banking clients: Verify template contains NO URLs (RBI 2024 mandate)
☐ Banking clients: Verify OTP is numeric only (no letters or special characters)

Security Tests

☐ OTP generator uses CSPRNG (not random.randint() in Python, not Math.random() in JS)
☐ OTPs are stored hashed (or not stored — using Techto Verify API instead)
☐ Expiry enforcement works — test with expired OTP, verify rejection
☐ Attempt limiting works — test with 4+ wrong OTPs, verify blocking after 3 failures
☐ Rate limiting works — test 4+ OTP requests in 10 minutes from one number
☐ OTP value is NOT returned to client in the API response (server-side only)

Delivery Tests

☐ Test send to Jio number — verify delivery in under 3 seconds
☐ Test send to Airtel number — verify delivery in under 4 seconds
☐ Test send to Vodafone Idea number — verify delivery in under 5 seconds
☐ Test send to BSNL number — verify delivery in under 6 seconds
☐ Webhook callback received and processed correctly for DELIVERED status
☐ Webhook callback processed for FAILED status — fallback logic triggered
☐ Voice OTP fallback tested — verify it triggers after configured timeout
☐ Test with DND-registered number — verify delivery (SI route is DND-exempt)

User Experience Tests

☐ Countdown timer displays correctly in UI
☐ Resend OTP button appears only after cooldown period
☐ Input field accepts 6 digits only (no letters, no special characters)
☐ Auto-submit works on 6th digit entry (optional but improves UX)
☐ Error messages are clear: "OTP expired", "Incorrect OTP", "Too many attempts"
☐ SMS auto-read (Android SMS Listener API or SMS User Consent API) tested if implemented

Error Handling Tests

☐ Invalid phone number format handled gracefully
☐ Network timeout handled — retry logic or fallback message displayed
☐ API authentication error handled — meaningful error message (not raw API error)
☐ DLT template mismatch error handled — alert triggered to your operations team
☐ Concurrent OTP requests from same number handled correctly

Delivery Performance Benchmarks — Techto Networks OTP India 2026

Network	Average Delivery	95th Percentile	99th Percentile
Jio	1.2 seconds	2.1 seconds	2.8 seconds
Airtel	1.4 seconds	2.4 seconds	3.1 seconds
Vodafone Idea	1.7 seconds	2.9 seconds	3.6 seconds
BSNL	2.1 seconds	3.4 seconds	4.2 seconds
All networks (weighted avg)	1.5 seconds	2.6 seconds	3.4 seconds

These benchmarks are measured on the dedicated OTP priority route — a channel reserved exclusively for authentication-grade traffic, separate from all promotional and transactional queues. They remain consistent regardless of promotional campaign volume on the platform.

API Error Code Reference — What Every Error Means and How to Fix It

Error Code	Message	Cause	Fix
DLT_TEMPLATE_MISMATCH	Content does not match registered template	Message content deviates from approved DLT template	Review template and ensure message variables populate correctly
INVALID_SENDER_ID	Sender ID not registered or wrong category	Sender ID used for SI category not approved	Register correct SI Sender ID via Techto compliance team
TEMPLATE_ID_REQUIRED	No template_id provided	API call missing template_id parameter	Add "template_id": "1007XXXXXXXXXX" to every API call
RATE_LIMIT_EXCEEDED	Too many requests	More than allowed OTP sends to same number in window	Implement client-side rate limiting; wait before retry
INVALID_PHONE_NUMBER	Number format invalid	Phone not in Indian format (91XXXXXXXXXX)	Validate and format: always include country code 91
INSUFFICIENT_CREDITS	Account balance too low	Credit balance exhausted	Top up credits in Techto dashboard
VOICE_FALLBACK_FAILED	Voice call not connected	Number unreachable or rejected call	Log failure; consider alternate auth method
OTP_EXPIRED	Verification attempted on expired OTP	User took longer than expiry window	Prompt user to request new OTP
MAX_ATTEMPTS_EXCEEDED	Too many failed verification attempts	3+ incorrect OTPs entered	Block number temporarily; require re-request

H2 — Pricing — OTP SMS API Integration India 2026

Plan	Price/OTP	Monthly Volume	Integration Features
Starter	₹0.14	Up to 50,000	REST API, OTP Verify API, voice fallback, sandbox, all SDKs
Growth	₹0.12	50K–5L	Everything + webhook callbacks, priority support, advanced rate limiting
Enterprise	₹0.10	5L+	Everything + SMPP, dedicated account manager, SLA uptime, SIM swap detection

All plans include:

DLT charges fully included — TRAI's ₹0.025/message in the price
OTP priority route — dedicated, never shares queue with promotional traffic
OTP Verify API — verify OTPs against our system without storing them yourself
Voice OTP fallback in 10 Indian languages — Hindi, English, Tamil, Telugu, Kannada, Malayalam, Marathi, Bengali, Gujarati, Punjabi
Sandbox environment — test full send-verify-webhook flow at no cost
Free DLT registration — SI category template registration for all OTP templates
Lifetime credit validity — credits never expire
Android, iOS, Flutter, React Native SDKs
24/7 support — WhatsApp, phone, email

Frequently Asked Questions — OTP SMS API Integration India 2026

Q: What is the correct way to generate a secure OTP in Python for India? Use Python's secrets module — specifically secrets.randbelow(900000) + 100000 for a 6-digit OTP. Never use random.randint() — Python's random module uses a Mersenne Twister PRNG which is not cryptographically secure and can be predicted by an attacker with sufficient OTP samples. The secrets module uses the operating system's CSPRNG (equivalent to reading from /dev/urandom), which is appropriate for security-critical applications.

Q: What TRAI DLT category does OTP SMS fall under in India? OTP SMS falls under the Service Implicit (SI) category — not Transactional (T). Registering under the wrong category causes your OTP messages to route through slower transactional queues instead of the dedicated OTP priority route. The SI category is DND-exempt, delivers 24/7, and uses a locked template format (OTP code, app name, and expiry only). Techto Networks registers all OTP templates under the correct SI category.

Q: Are URLs allowed in OTP SMS messages in India? For general OTP messages (app login, account verification), URLs are permitted where they serve a functional purpose. For banking and payment OTPs, RBI's 2024 circular explicitly prohibits URLs — enforced at the operator level. Banking OTP templates containing URLs are blocked before delivery. Always use banking-specific templates without URLs for any payment authentication flow.

Q: How do I prevent OTP bombing — where attackers trigger hundreds of OTPs to a victim? Implement rate limiting at two levels: (1) Application level — maximum 3 OTP requests per phone number per 10-minute window, enforced with Redis or in-memory cache; (2) API level — pass max_resends: 3 and resend_cooldown_seconds: 60 in your Techto OTP API call. At the infrastructure level, Techto Networks' platform detects anomalous OTP request patterns and flags suspicious sends to your account's security dashboard.

Q: How fast does OTP SMS deliver in India with Techto Networks? Techto Networks' dedicated OTP priority route delivers in 1.2 seconds average on Jio, 1.4 seconds on Airtel, 1.7 seconds on Vodafone Idea, and 2.1 seconds on BSNL — for a weighted all-network average of 1.5 seconds. The 99th percentile (slowest 1% of deliveries) is under 4.2 seconds on any Indian network.

Q: Should I store the OTP in my database? If using Techto Networks' OTP Verify API — no. Pass the message_id returned from the send call to the verify endpoint when the user submits their OTP, and Techto's system handles verification without you storing the code. If implementing local verification, store only a salted SHA-256 hash of the OTP — never the plaintext. Delete the record immediately after successful verification or expiry.

Q: What happens when OTP SMS delivery fails? How do voice OTP fallback works? Pass "voice_fallback": true and "fallback_after_seconds": 30 in your OTP API call. If SMS is not delivered within 30 seconds (configurable), Techto's system automatically initiates an outbound call to the same number. An automated IVR reads the OTP aloud in your chosen language. Your webhook receives a VOICE_INITIATED event. No separate integration required — voice fallback is native to the platform.

Q: How do I test my OTP SMS integration before going live in India? Techto Networks provides a full sandbox environment — activated at account creation with no credit card required. In sandbox mode, you can test the complete send-verify-webhook flow using test phone numbers. SMS delivery is simulated; webhooks fire with realistic delay patterns. Switch from sandbox to production API credentials when your full testing checklist (DLT compliance, security, delivery, and error handling tests) is complete.

Ready to Integrate India's Fastest OTP SMS API?

Your users are waiting for their OTP. In India's payments-first digital economy, 1.5 seconds average delivery, TRAI DLT compliance built in from day one, voice fallback in Hindi and 9 other languages, and cryptographically secure implementation patterns — this is the OTP SMS API integration that production Indian applications deserve.