The best OTP API providers in 2026 are SMS.to, Twilio Verify, Vonage Verify, Sinch Verification, Infobip, Plivo Verify and Telnyx Verify. All seven send one-time passcodes by API; the real differences are how they bill (per successful verification, per attempt or channel fees only), which channels they fall back to, and how much fraud protection comes included.
Every competitor fact below was checked on the provider’s own website in September 2026 and is linked. SMS.to is our own product, so its entry sticks to what our OTP verification API page states.
How do the top OTP API providers compare?
Prices are published list prices as of September 2026; channel rates vary by country for every provider.
| Provider | OTP channels (as published) | Pricing model | Named fraud controls |
|---|---|---|---|
| SMS.to Verify | SMS, WhatsApp, Viber, Telegram, with automatic fallback | Channel fee (WhatsApp, Viber, Telegram only if delivered; SMS when sent) plus a Verify fee only when the user verifies | Fallback orchestration, HLR and MNP lookup, recommended rate limits |
| Twilio Verify | SMS, WhatsApp, voice, email, push, TOTP, passkeys, Silent Network Auth | $0.05 per successful verification plus channel fees | Fraud Guard |
| Vonage Verify | SMS, RCS, WhatsApp, voice, email, Silent Authentication | €0.052 / $0.06084 per successful verification plus messaging and voice rates, or an all-in “Verify Success” plan via sales | Fraud Defender Advanced (included) |
| Sinch Verification | SMS, flash call, phone call, data verification | Per request: fixed price per flash call attempted, SMS price per SMS attempt | Not named on the product page |
| Infobip | SMS, WhatsApp, voice, email, RCS, Viber, silent mobile verification | Pay as you go for SMS; authentication rates via calculator or sales | Signals, SIM swap detection |
| Plivo Verify | SMS, voice, WhatsApp | $0 verification fee; you pay channel rates only | Fraud Shield (included) |
| Telnyx Verify | SMS, voice, flash call, silent auth, WhatsApp | $0.03 per successful verification plus channel costs; $0 platform fee | Not named on the pricing page |
What pricing models do OTP APIs use?
OTP pricing looks similar on a landing page and very different on an invoice. There are four models:
- Verification fee plus channel fee. Twilio, Telnyx and Vonage Verify Conversion charge a fee when the user completes verification, plus the channel cost of each attempt.
- Channel fees only. Plivo publishes a $0 verification fee.
- Per attempt. Sinch prices verification per request, successful or not.
- Pay on outcome. Vonage’s Verify Success plan charges only for successful verifications, with no charge for unsuccessful attempts. SMS.to charges WhatsApp, Viber and Telegram only if they deliver, and the Verify fee only when the code is confirmed.
The number to compare is cost per verified user, not cost per message. A simple way to estimate it: (channel price x average attempts per user) + verification fee. On Twilio’s published US list prices, one SMS attempt costs $0.05 + $0.0083 = $0.0583 per verified user; if the user asks for a resend, it becomes $0.05 + (2 x $0.0083) = $0.0666. Run the same sum for your top countries, because channel rates vary widely outside the US.
The 7 best OTP API providers in 2026
1. SMS.to Verify: best for multichannel OTP with pay-on-verify billing
SMS.to is run by Intergo Telecom, a licensed telecom and CPaaS operator in Cyprus building messaging infrastructure since 2014. Its Verify API sends one-time passcodes over SMS, WhatsApp, Viber and Telegram. You set the channel order, expiry, code length or format, templates and language once in a Verify App, then override any of them on a single request for a test or a new region.
If the first channel does not deliver within your timeout, Verify falls back to the next one automatically, and your logs show the path each code took. You can also bring your own code (client-generated OTP). A request with WhatsApp first and SMS as the safety net:
curl -X POST https://verifyapi.sms.to/api/v1/verifications/create \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"guid": "3-1748345-bcef-0342-6bef5c26-04f64e7",
"recipient": "+35799999999",
"callback_url": "https://example.com/verify/callback",
"channels": [
{ "channel": "whatsapp", "priority": 1, "expiry_time": 30 },
{ "channel": "sms", "priority": 2, "expiry_time": 30 }
]
}'The guid is your Verify App’s identifier. When the user types the code, you check it with POST https://verifyapi.sms.to/api/v1/verifications/confirm.
Consider: Verify does not list voice, email or silent authentication channels, so teams that need those will look at Twilio, Vonage or Infobip.
2. Twilio Verify: best for the widest range of verification methods
Twilio Verify covers SMS, WhatsApp, voice and email through one API, plus passkeys, Silent Network Auth, TOTP authenticator apps, push and silent device approval, according to its Verify product page. Twilio says Verify handles carrier and regulatory changes in 200+ countries and regions, and positions its Fraud Guard feature against SMS pumping.
The published list price as of September 2026 is $0.05 per successful verification plus channel fees: in the US that is $0.0083 extra per SMS and $0.0034 per WhatsApp authentication template message, while push and TOTP are included. Volume pricing is by quote.
Consider: channel fees apply to each attempt, so resends add up in high-cost countries.
3. Vonage Verify: best for outcome-based pricing
Vonage Verify supports SMS, RCS, WhatsApp, voice (text-to-speech), email and Silent Authentication, which confirms the number through the mobile network without a code, per its Verify page. It can resend a PIN by voice automatically in one API request, and Fraud Defender Advanced, which adds protection against artificially inflated traffic, is included at no extra cost.
Vonage publishes two pricing models. Verify Conversion is €0.052 / $0.06084 per successful verification, with messaging and voice rates added for attempts (published list price as of September 2026). Verify Success charges only for successful verifications, all in, with rates through sales.
4. Sinch Verification: best for flash call and data verification
Sinch offers four methods on its Verification API page: SMS, flash call (a missed call whose caller ID is the code), phone call and data verification. Its developer documentation describes data verification as using the telephony provider’s infrastructure to verify the number without user interaction, and notes automatic SMS code extraction on Android.
Billing is per request: a fixed price for each flash call attempted and a country- and operator-based SMS price for each SMS attempt. The price list sits in the Sinch dashboard rather than on the page.
Consider: WhatsApp is not listed as a Verification API method, and per-attempt billing means failed attempts cost money.
5. Infobip: best for enterprise omnichannel authentication
Infobip’s authentication product delivers OTPs over SMS, WhatsApp, voice, email, RCS and Viber, alongside silent mobile verification. Its Signals feature blocks fraudulent SMS traffic, and the suite adds SIM swap detection, number lookup and multistep failover.
Infobip’s pricing page describes SMS as pay as you go and gives WhatsApp authentication and Viber OTP rates through interactive calculators; there is no single published per-verification price.
Consider: the breadth suits large, multi-region programmes; expect a sales-led setup.
6. Plivo Verify: best for avoiding a verification fee
Plivo’s Verify pricing lists $0 for OTP verification and $0 for Fraud Shield, its AI-driven pumping protection, so you pay only SMS, voice or WhatsApp channel rates (published list price as of September 2026). Its product page lists SMS, voice and WhatsApp today, with RCS and email marked as coming soon, plus configurable code length and expiry (three minutes by default).
Consider: with no verification fee, the channel rate is the whole price, so compare it country by country.
7. Telnyx Verify: best for teams already on Telnyx’s network
Telnyx’s Verify pricing page lists $0.03 per successful verification over SMS, voice, flash call or WhatsApp, plus channel costs (“$0.03 per successful verification + SMS API pricing” on the page), and headlines “from $0.05 a verification” overall. Pay as you go has a $0 platform fee; committed plans start at $500 a month.
Telnyx says it holds carrier licences in 30+ countries and runs a privately owned fibre backbone between its points of presence.
Consider: the page does not name a fraud-protection feature for Verify, so ask how pumping is handled.
How do you choose the right OTP API provider?
From the operator side, most OTP problems come from routing, fallback timing and fraud, not the API itself. Check these before you sign:
- Price your real traffic. Calculate cost per verified user for your top destinations, including resends. A $0 verification fee on an expensive SMS route can cost more than a fee-based plan on a cheaper one.
- Test fallback timing. A fallback that waits too long loses the user; one that fires too early sends two codes and doubles the channel cost. Look for timeouts you can set per channel and per request.
- Ask how failed attempts are billed. SMS is usually charged when it is sent, whether or not it arrives (that is how SMS.to bills it), while some app channels are billed only on delivery.
- Plan for SMS pumping. Built-in tools such as Fraud Guard, Fraud Defender, Fraud Shield and Signals help, but add your own rate limits per number, IP and device, and block prefixes you do not serve. A country where sends climb while completed verifications stay flat is the pattern to alert on.
- Check sender registration. Many countries require registered sender IDs or templates for OTP traffic, such as DLT registration for SMS to India. Ask who does the paperwork.
- Demand per-attempt visibility. Your support team needs the delivery report and channel for every attempt to answer “why didn’t my code arrive?”.
- Match channels to regions. Start with WhatsApp or Viber where they are widely used and keep SMS as the fallback. Our guide on how to choose a Verify API for phone verification and 2FA goes deeper.
How SMS.to handles OTP verification
The SMS.to Verify API keeps your defaults in one Verify App, and every step is logged and sent to your webhooks, so support, product and engineering see the same record. Billing follows the outcome:
- WhatsApp delivers the code to a user in India: you pay the WhatsApp send plus the Verify success fee.
- WhatsApp times out for a user in Egypt and SMS delivers: you pay the SMS send plus the Verify success fee.
- SMS delivers but the user never enters the code: you pay the channel fee, with no success fee.
For fraud, pair rate limits and shorter expiry for risky actions with an HLR and MNP lookup to keep numbers clean. For the full journey, see how to build an OTP flow with smart fallback and the benefits of a multichannel Verify API.
FAQs
Which OTP API provider is the cheapest?
No provider is cheapest everywhere. On published list prices, Plivo charges no verification fee, Telnyx charges $0.03 and Twilio $0.05 per successful verification, but all add channel costs that vary by country. Compare cost per verified user for your own destinations.
What does “pay per successful verification” mean?
You pay the verification fee only when the user enters the correct code. Channel fees for each attempt usually still apply, as with Twilio, Telnyx and Vonage Verify Conversion. SMS.to charges app channels only if they deliver and SMS when it is sent.
Is SMS OTP still secure enough in 2026?
For most sign-up and login flows, yes, when paired with short expiry, rate limits and fraud monitoring. For high-risk actions, add a stronger second factor: several providers now offer silent network authentication, passkeys or TOTP.
What is the difference between an OTP API and an SMS API?
An SMS API sends any text you give it. An OTP or Verify API also generates the code, handles expiry, retries and fallback, and checks the code the user enters.
Can I send OTPs over WhatsApp or Viber?
Yes. SMS.to supports WhatsApp, Viber and Telegram with SMS fallback; Twilio, Vonage, Plivo and Telnyx list WhatsApp; Infobip lists both WhatsApp and Viber. SMS fallback covers users who do not have the app installed.
Want to test pay-on-verify billing and fallback on your own traffic? Create a free account, no credit card needed.
