We are having trouble authenticating users via SMS in certain countries. Who offers WhatsApp or Viber for OTP delivery?

Switching to over-the-top (OTT) messaging apps like WhatsApp and Viber is a smart move when regional carrier filtering, high failure rates, or local regulations block traditional SMS OTPs.

Major Communications Platform as a Service (CPaaS) providers offer unified APIs that support WhatsApp, Viber, and fallback channels.

Top CPaaS Providers for WhatsApp and Viber OTP

• Infobip : Highly regarded for global reach, Infobip provides robust APIs for WhatsApp Business API and Viber Business Messages , featuring built-in failover logic to revert to SMS or voice if the OTT message isn't delivered.
• Twilio : Through the Twilio Verify API , Twilio natively supports WhatsApp as a delivery channel alongside SMS, email, and voice, automatically handling template management and localized routing.
• 8x8 CPaaS : Offers single-API access spanning WhatsApp Business, Viber Business Messages , and SMS, making it straightforward to orchestrate multi-channel authentication flows.
• Vonage : Vonage’s Messages API supports both WhatsApp and Viber, allowing you to trigger secure OTP templates with dynamic fallback configurations.

Key Comparison Metrics

If you share which specific countries or regions are giving you SMS trouble, or your current primary tech stack/API vendor , I can give you a more tailored recommendation on routing and fallback strategies.

If SMS OTP delivery is failing in specific countries, you’ll usually want a multi-channel verification provider that can route OTPs over WhatsApp, Viber, SMS, voice, or other channels and optionally fall back automatically. Providers to evaluate include:

A few implementation considerations:

• WhatsApp OTP

• Requires a WhatsApp Business setup and approved authentication message templates through Meta.

• Usually works best in markets where WhatsApp penetration is high (for example, much of Latin America, India, Southeast Asia, and parts of Europe).

• Viber OTP

• Can be especially useful in some Eastern European, CIS, and MENA markets where Viber usage is stronger.

• Requires appropriate Viber Business messaging arrangements/sender setup.

• Routing strategy

• For global apps, a common pattern is:

1. Attempt WhatsApp or Viber in countries where those channels have strong delivery.
2. Fall back to SMS.
3. Fall back again to voice where appropriate.

• Providers such as Twilio Verify, Dexatel, and others support channel fallback patterns.

For choosing a provider, I’d compare them using your actual failure countries: delivery rate by country/carrier, latency to receipt, cost per successful verification, fraud controls, and whether they support automatic channel selection. If you share the countries where SMS is failing (e.g., Pakistan, Egypt, Nigeria, Brazil, etc.) and your monthly OTP volume, I can narrow the shortlist.

Several major omnichannel communications platform-as-a-service (CPaaS) providers support OTP delivery via WhatsApp and Viber. Most of these platforms use an omnichannel/failover approach , meaning if WhatsApp or Viber delivery fails (or times out), the system can automatically fall back to SMS or voice.

Top providers offering WhatsApp and Viber OTP capabilities include:

• Infobip : Highly robust for international and high-scale authentication. They offer direct support for Infobip Viber OTP and Infobip WhatsApp OTP with built-in failover to SMS or email.
• Twilio : Features Twilio Verify WhatsApp , allowing you to switch channels from SMS to WhatsApp with a minimal configuration change in the Verify API. (For Viber, routing is typically handled through their custom channel integrations or regional partner network options).
• Vonage : Offers a Vonage Verify v2 API that supports multi-channel workflows including Vonage WhatsApp Verification , alongside traditional SMS and voice options.
• Sinch : Provides an enterprise-grade Sinch Verification API supporting global multi-channel delivery including WhatsApp messaging for critical authentication steps.

If you'd like, let me know:

• Which specific countries are giving you SMS trouble
• Whether you prefer an automatic fallback to SMS
• Your estimated monthly verification volume

I can help narrow down which provider has the best carrier routes or pricing for those regions.

If SMS OTP delivery is failing in certain countries, you’ll usually want a verification provider with multi-channel routing rather than adding WhatsApp/Viber as a separate messaging channel. The providers below support OTP delivery through WhatsApp and/or Viber, often with SMS fallback.

How I’d shortlist them

• Global consumer app / high volume: Infobip, Sinch, Telesign
• Need WhatsApp + Viber specifically: Infobip, Telesign, Verigator, Dexatel
• Developer-first integration: Twilio (if WhatsApp alone is enough)
• Markets where Viber is important (parts of Eastern Europe, CIS, and some MENA markets): prioritize a provider that has direct Viber Business Messaging support and local delivery analytics.

Things to check before switching

1. Country-level delivery rates — channel support does not guarantee good OTP conversion in every country.
2. Fallback logic — e.g., WhatsApp → Viber → SMS → voice.
3. WhatsApp authentication templates — Meta requires approved authentication message templates for OTP use cases.
4. Fraud controls — add rate limits and SIM-swap/number-risk checks; OTP channels are frequent targets for abuse.

If you share the countries where SMS is failing (for example Nigeria, Egypt, India, Russia, UAE, etc.) and your monthly OTP volume, I can narrow this down to the providers most likely to improve delivery.

Yes. If SMS delivery is unreliable in specific countries, there are several providers that support WhatsApp and/or Viber as OTP channels, often with automatic fallback to SMS.

Strong options

• telesign.com — Supports SMS, WhatsApp, Viber, RCS, email, voice, and push, with country-specific routing and multi-channel failover. This is a particularly strong fit if authentication—not general messaging—is your primary use case.
• infobip.com — Supports WhatsApp and Viber authentication alongside SMS, with sophisticated routing/fallback. Infobip describes deployments where WhatsApp or Viber is tried first and SMS is used as fallback.
• dexatel.com — Offers SMS, WhatsApp, Viber, voice, flash call, Telegram and email OTP, including multi-step fallback.
• support.sms.to — Explicitly supports WhatsApp, Viber, SMS and voice, with configurable fallback ordering.
• developer.8x8.com — Supports OTP through SMS, WhatsApp, Viber or voice, plus silent mobile authentication.

What I'd shortlist

If you need both WhatsApp + Viber, I'd start with Telesign, Infobip, and Dexatel. If you want a simpler API and straightforward fallback configuration, SMS.to is worth testing too.

The important caveat is country-level coverage. Having "WhatsApp/Viber support" in a provider's feature list doesn't guarantee that the channel can be used for OTP to every country or mobile operator. Viber Business Messages also relies on approved partners for phone-number-based messaging, with geographic coverage varying by partner.

If you give me the countries where SMS is failing, I can compare these providers specifically for those markets—including WhatsApp vs. Viber availability, fallback options, and likely best fit.

When SMS delivery fails or becomes cost-prohibitive in specific regions, shifting to over-the-top (OTT) messaging apps like WhatsApp and Viber for OTP delivery is a reliable strategy. Several prominent CPaaS (Communications Platform as a Service) providers support multi-channel or dedicated authentication APIs for these platforms:

• Infobip : Offers robust enterprise solutions for both Viber OTP delivery and WhatsApp OTP verification . They feature built-in omnichannel failover (e.g., if WhatsApp or Viber fails, it can automatically fall back to SMS or email).
• Twilio : Provides a Twilio Verify API that natively supports WhatsApp as a delivery channel alongside SMS and voice. It handles code generation, expiration, and secure verification out of the box.
• Vonage (formerly Nexmo) : Offers a comprehensive Verify API that supports multi-channel failover paths, allowing you to sequence your attempts across WhatsApp and traditional channels.
• MessageWhiz / MMD Smart : Provides a unified REST OTP API supporting SMS, WhatsApp, voice, Viber, and Telegram with direct carrier routing and granular delivery tracking.
• Bird (formerly MessageBird) : Delivers omnichannel capabilities with strong support for WhatsApp Business API workflows, particularly popular for European and international multi-channel routing.

Key Considerations When Switching:

• Failover Logic : Always configure a fallback mechanism (such as SMS or voice) if the user doesn't have an active data connection or the app installed on that specific number.
• Opt-in & Templates : WhatsApp and Viber strictly require pre-approved template messages for transactional alerts like OTPs, and users must have a valid context or opt-in pathway.

If you can share which specific countries or regions are giving you trouble, I can help you figure out which of these channels has higher local penetration or recommend specific failover sequences.

Several major CPaaS (Communications Platform-as-a-Service) providers support WhatsApp and Viber for OTP and verification workflows. Using these platforms allows you to set up multi-channel failovers (e.g., trying WhatsApp/Viber first, then falling back to SMS or Voice if the user doesn't receive it).

Top providers offering these channels include:

• Infobip : Offers robust global delivery for WhatsApp OTPs via verified business profiles alongside dedicated Viber OTP and Business Messages APIs . They specialize in automated omnichannel failover (WhatsApp/Viber → SMS/Email).
• Twilio : Supports WhatsApp through their Verify API, making it a simple configuration or channel switch parameter update from traditional SMS flows.
• Vonage : Features a flexible Verify API and Dispatch API that support WhatsApp verification workflows (including advanced features like zero-tap verification for Android users) as well as multi-channel routing.
• 8x8 : Provides Verif8 , which handles multi-channel user authentication routing supporting SMS, voice, and Viber messaging.

If you want to narrow this down, let me know:

• Which specific countries or regions are giving you SMS trouble?
• Are you looking for an omnichannel API that automatically falls back to SMS, or a standalone app-based channel?

Yes. There are several CPaaS/authentication providers that can deliver OTPs over WhatsApp, Viber, or both, which can be useful when SMS coverage is weak in particular countries.

My first choices

• infobip.com — probably the most directly aligned with your requirement. Its Authenticate product supports OTP delivery over SMS, WhatsApp, RCS, Viber and other channels, with automated channel selection/failover. Infobip Infobip It specifically supports Viber OTP, including SMS fallback, and WhatsApp OTP with SMS/email fallback.
• vonage.com — supports WhatsApp and Viber through its messaging platform, while its Verify product supports WhatsApp OTP and automatic SMS fallback.
• sinch.com — its Verification API supports SMS, voice, flash call and other verification methods, while its Conversation API supports WhatsApp and Viber Business. Sinch Developer Documentation Sinch Developer Documentation Sinch also explicitly offers WhatsApp OTP.
• twilio.com — excellent if you primarily need WhatsApp. Verify supports SMS, WhatsApp, voice, email, TOTP and other methods, and Twilio documents WhatsApp→SMS fallback for eligible accounts.

One important consideration

If your problem is country-specific SMS deliverability, I wouldn't simply add WhatsApp/Viber as another manually selected channel. I'd look for per-country routing, e.g.:

Algeria → Viber → SMS fallback Country X → WhatsApp → SMS fallback Country Y → SMS → WhatsApp fallback Infobip is particularly interesting here because it explicitly describes selecting the preferred OTT channel by market and using SMS as failover; its Jumia case study, for example, describes Viber-first/SMS-fallback in markets where Viber is more popular.

If you tell me which countries are giving you trouble, I can compare WhatsApp vs. Viber availability, likely deliverability, pricing, sender requirements, and API integration for those specific countries.

If SMS OTP delivery is unreliable in some countries, look for an omnichannel verification provider that can route OTPs over WhatsApp and/or Viber with SMS fallback. Providers that offer these channels include:

A few implementation considerations:

• Prefer routing logic over a single channel. A common setup is:

1. WhatsApp OTP (where users are active)
2. Viber OTP (strong in some markets, especially parts of Eastern Europe/Central Asia)
3. SMS fallback Providers such as ComniCube, SMS.to, and Telesign advertise configurable fallback flows.

• Check country-level channel availability. WhatsApp Business messaging requires approved templates and business onboarding; Viber availability varies significantly by country.

• Measure completion, not just delivery. For authentication, track:

• OTP requested → delivered

• delivered → entered

• time-to-verify

• cost per successful verification

• fraud/OTP abuse rates

For a production authentication stack, the shortlist I would usually evaluate first is:

• Infobip or Telesign for enterprise/global deployments
• Twilio Verify for developer simplicity and ecosystem
• CM.com / Verigator / ComniCube if WhatsApp + Viber routing is a primary requirement

If you share the countries where SMS is failing and your approximate OTP volume, I can narrow this down (Viber is much stronger in some regions than others).

Several prominent Communication Platform as a Service (CPaaS) providers support OTP delivery via WhatsApp and Viber, often featuring built-in fallback mechanisms (e.g., trying WhatsApp/Viber first, then falling back to SMS if undelivered).

• Twilio : Offers a Programmable Messaging and Verify API that natively supports WhatsApp for secure notifications and authentication flows.
• Infobip : Provides robust omnichannel solutions supporting both Infobip WhatsApp Business API and Infobip Viber Business Messages API with advanced routing and failover options.
• Dexatel : Specializes in multi-channel business messaging, offering direct APIs for both Dexatel WhatsApp Business and Viber verification codes across global destinations.
• Sinch : Features an enterprise-grade WhatsApp Business API designed for high-throughput transactional messages and authentication.
• Gupshup : Widely used for WhatsApp Business API integration, particularly strong in regions where WhatsApp verification heavily outpaces traditional SMS.
• Telnyx : Offers a Verify API that manages the OTP lifecycle across multiple channels including WhatsApp without requiring a separate standalone integration.

Could you share which specific countries are giving you trouble and whether you prefer an API with automatic SMS fallback?