OTP SMS for Login and Verification in Your App or Website

How OTP SMS for login and verification works

Your server creates a random code, stores a hash of it with an expiry time, and calls our API with the user's number and the code as a template variable. We route it to the operator and return a message ID. When the user enters the code, your server checks it against the stored hash and marks the number as verified. OTP SMS for login and verification is typically delivered in a few seconds.

Common uses include sign-up, login, password reset, changing a registered mobile or email, confirming a payout, and verifying a cash on delivery order. Each use should have its own template so the user knows exactly what they are approving.

Template rules for OTP messages

OTP templates have a few fixed requirements under DLT and some good habits worth following.

• Register the OTP template under the correct category on your DLT portal, with the code as a {#var#} field.
• State the purpose: login, sign-up or payment of a stated amount.
• Include the validity period, for example 5 or 10 minutes.
• Add a warning not to share the code, and never ask users to reply with it.
• For Android autofill, end the template with your app's 11-character SMS Retriever hash.

Security practices for your OTP flow

Use 4 to 6 digit codes generated with a secure random function, and expire them within 10 minutes. Allow only a few wrong attempts before you lock the code. Do not write OTPs to plain-text logs or analytics tools.

Protect the send endpoint. Bots can hit your sign-up form and trigger thousands of OTPs to premium or random numbers, which wastes credits. Limit requests per number, per IP address and per device, add a CAPTCHA after repeated attempts, and watch for sudden spikes in one number series. Our MIS reports make unusual traffic easy to spot.

Choosing the right OTP sender setup

Use one header for all OTPs so users learn to trust it, and keep promotional traffic on a different header. If you run several apps or brands, give each its own OTP template that names the brand, because users who see an unknown name may ignore the code.

For high-volume apps, send OTPs through our HTTPS API with a timeout and a retry on a second route only if the first call fails. Do not resend the same code in a loop. Generate a fresh code on each resend and invalidate the older one.

When to offer voice, WhatsApp or RCS for OTP

Most users receive SMS OTPs without trouble. A few will not, because of weak signal, a full inbox or roaming. Offer a resend after 30 seconds, then a voice OTP call that reads the code aloud. Users who are active on WhatsApp can get an authentication message at ₹0.12 to ₹0.16 on our plans. RCS OTP is also available on Jio, at tiered rates set by the operator. Always keep SMS as the default, because it works on every phone without data.

Measure your OTP success rate as verified logins divided by codes sent. If it drops, check delivery reports by operator and circle first, then check your own app flow.