Quick Answer
An OTP API lets your application send a one-time password to a user's phone and verify identity in real time. With SMSGatewayHub, your server generates the code and calls the SendSMS endpoint with your API key, DLT entity ID and OTP template ID; the code is delivered on a transactional (-T) route that reaches DND numbers 24/7, and a delivery report comes back for every message. WhatsApp, voice and RCS can be added as fallback channels.
How an OTP API works
Seven steps happen in a few seconds every time a user logs in or signs up.
| Step | Where it happens | What to get right |
|---|
| 1. User enters a mobile number | Your app or website | Validate the format and apply resend limits. |
| 2. Server generates the code | Your backend | Random 4-8 digit code, stored hashed with an expiry. |
| 3. API call to send the OTP | SMSGatewayHub API | Use your DLT entity ID, transactional header and OTP template ID. |
| 4. DLT scrubbing and routing | Operator DLT platform | Text must match the registered template exactly. |
| 5. Delivery to the handset | Mobile operator | -T route reaches DND numbers 24/7. |
| 6. User enters the code | Your app or website | Android auto-read can fill it for the user. |
| 7. Server verifies | Your backend | Compare, expire the code and log the delivery report. |
Sample OTP SMS API request
Send an OTP with a single HTTPS call. Replace the placeholders with values from your panel and your approved DLT template.
cURL
curl -G "https://www.smsgatewayhub.com/api/mt/SendSMS" \
--data-urlencode "APIKey=YOUR_API_KEY" \
--data-urlencode "senderid=ABCDEF" \
--data-urlencode "channel=OTP" \
--data-urlencode "number=9198XXXXXXXX" \
--data-urlencode "text=482913 is your OTP to log in to ABC App. Do not share it. - ABC" \
--data-urlencode "EntityId=YOUR_ENTITY_ID" \
--data-urlencode "dlttemplateid=YOUR_TEMPLATE_ID"
A successful call returns ErrorCode 000 and a JobId you can match against the delivery report. Full parameters and PHP, Python, JavaScript and C# samples are in the developer API docs; you can also use the HTTP API, HTTPS API or SMPP API.
One OTP API, five verification channels
Start with SMS and add channels for users that SMS cannot reach quickly.
| Channel | Best for | Learn more |
|---|
| SMS OTP | Default for every Indian mobile, no app or data needed | OTP SMS service provider |
| WhatsApp OTP | Users who prefer WhatsApp; copy-code and one-tap buttons | WhatsApp OTP API |
| Voice OTP | Landlines, feature phones and SMS retry | Voice OTP |
| Missed call verification | Number ownership checks without typing a code | Missed call OTP |
| RCS | Branded, verified codes in the native Messages app | RCS messaging |
Why developers choose the SMSGatewayHub OTP API
A late OTP is a lost sign-up. These are the things that keep codes arriving on time.
Priority transactional routes
Multi-operator routing with failover gives 2-6 second typical delivery and a 99.9% uptime SLA.
Real delivery reports
Operator delivery status for every code in the panel and API. See live delivery reports.
Certified security
ISO 27001, ISO 9001:2015, SOC 2 and VAPT tested, with OTP content masked in reports.
Trusted since 2009
10,000+ registered businesses and 2,000+ enterprise clients, with 24/7 support.
OTP API use cases by industry
How to integrate the OTP API
Get your API key
Create a free account and copy your API key from the panel.
Complete DLT
Register your entity, a transactional sender ID and OTP templates through DLT registration.
Call SendSMS
Send the code from your backend with the entity ID and template ID on every request.
Handle reports
Store the JobId and match delivery reports to retry or switch channel.
Add fallback
Enable WhatsApp, voice or missed call verification for numbers that keep failing.
TRAI DLT rules and security best practices
- Register OTP templates under the transactional category so they carry a -T suffix and reach DND numbers.
- Put the code in a {#numeric#} variable; never add offers, or the message becomes promotional.
- Whitelist any link or callback number as a CTA on DLT, or the message is blocked.
- Keep codes valid for a few minutes and say so in the message.
- Limit attempts and resends per number to stop SMS pumping and brute force.
- Keep your API key on the server, restrict it by IP and never return the code to the client.
Frequently Asked Questions
What is an OTP API?
An OTP API is an interface your application calls to send a one-time password to a user and verify their phone number. Your server generates the code, the API delivers it by SMS or another channel, and your server checks the code the user enters.
What is the difference between an OTP API and an OTP SMS API?
An OTP SMS API delivers codes only by SMS. An OTP API can cover several channels, such as SMS, WhatsApp, voice and missed call. SMSGatewayHub offers both from one account, with SMS as the default channel.
Do I need DLT registration to use an OTP SMS API in India?
Yes. Every commercial SMS in India is checked against TRAI DLT records, so you need a registered entity, a transactional header and an approved OTP template. The API request carries your entity ID and template ID.
Can OTP SMS reach DND numbers?
Yes. OTPs sent on transactional -T routes reach all Indian numbers, including DND, 24/7, as long as the template contains no promotional content.
How fast is the SMSGatewayHub OTP API?
OTP SMS is delivered in 2-6 seconds in typical conditions, using multi-operator routing with automatic failover and a 99.9% uptime SLA.
Which programming languages can I use?
Any language that can make an HTTPS request, including PHP, Python, Java, Node.js and C#. High-volume senders can also connect over SMPP. Code samples are in the developer API docs.
Integrate the OTP API in an afternoon
Get your API key, free DLT guidance and sample code, then send your first verification code today.