Send and Verify OTPs Through SMS
Add SMS verification to your app through one API that handles code generation, delivery, and verification, with automatic routing across your eligible channels.
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Reach Users Without Requiring a Messaging App
Send verification codes to mobile numbers through SMS, including users who cannot receive them through WhatsApp, Viber, or RCS.
Managed OTP Verification
Let SecondFactor generate and verify codes without building OTP storage and validation into your backend.
Cost-Based Routing
Evaluate SMS alongside your other enabled channels to select the lowest-cost eligible route for each request.
Automatic Fallback
Use SMS as a fallback when another channel doesn't confirm delivery and SMS is the next eligible route.
Delivery Logs and Costs
Check the destination, delivery status, and cost of each request to monitor usage and investigate delivery issues.
Add SMS Verification With Two API Calls
Complete the applicable sender and template setup, then connect your application to SecondFactor's send-and-verify API.
Request an OTP
Call /otp/send with the user's phone number to generate a code, request delivery, and receive a request ID.
Verify the Code
Call /otp/verify with the request ID and the code your user entered to receive the verification result.
Manage Your SMS Sender and Verification Templates
Set up your SMS messages through SecondFactor, with sender requirements based on the countries where you plan to deliver codes.
Sender Setup by Destination
Complete the sender registration required for your destination markets, including branded sender approval where applicable.
Custom OTP Messages
Create an SMS authentication template with your app name and verification code placeholder, then submit it for review.
Message Length and Encoding
Keep templates concise and review their encoding, since longer messages and some character sets can increase the number of billable SMS segments.
Use SMS OTPs for Signup and Account Access
Verify Phone Numbers at Signup
Ask new users to enter a code sent to their mobile number before completing registration.
Explore Phone Verification →Add a Second Authentication Step
Request an SMS code alongside another authentication factor, such as a password, before granting account access.
Explore Two-Factor Authentication →Check SMS OTP Pricing for Your Destination Markets
Review rates for the countries where your users are located, or contact our team about pricing for your expected verification volume.
Connect additional channels to give SecondFactor lower-cost routing options where they are available and eligible.
Frequently Asked Questions
Write to support@secondfactor.ai for anything not covered here.
Do Users Need an App or Internet Connection to Receive an SMS OTP?+
Users do not need a messaging app or mobile data connection to receive a standard SMS. They need a mobile number and access to SMS service, while completing verification in your application may require internet access.
Can I Use My Business Name as the SMS Sender?+
Branded sender availability depends on the destination. Some markets require registration and approval before your business name can appear as the sender.
Can I Customize the SMS Message?+
You can create an authentication template using your app name and OTP placeholder, subject to review and destination requirements. Message length and encoding can affect the number of SMS segments.
Will Every OTP Request Be Sent Through SMS?+
SecondFactor's routing engine selects the lowest-cost eligible channel for each request. If you enable additional channels, a request may use one of those instead of SMS.
Can SMS Be Used as a Fallback for WhatsApp?+
Yes, SMS can be used when WhatsApp delivery isn't confirmed and SMS is the next eligible channel. You need to enable SMS and complete any applicable sender and template setup.
What Happens if SMS Delivery Isn't Confirmed?+
SecondFactor attempts the next eligible channel after eight seconds without delivery confirmation. Fallback depends on another channel being enabled and available for the recipient.
How Much Does an SMS OTP Cost?+
Pricing depends on the destination and your pricing arrangement. Review the pricing page or contact our team to understand applicable charges, including how message segments and fallback are billed.
Can I Test SMS OTP Delivery Before Integrating?+
New accounts receive free credits to test real OTP delivery through the PIE Playground. The result shows which eligible channel handled your request, and you can enter the received code to test verification.
Start Testing Your SMS OTP Integration
Create an account to test OTP delivery, or talk to our team about SMS setup and pricing for your destination markets.