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

When SMS delivery fails or becomes cost-prohibitive in specific regions, shifting your One-Time Password (OTP) verification flow to over-the-top (OTT) messaging apps like WhatsApp and Viber is a reliable workaround.

Major CPaaS (Communications Platform as a Service) providers offer robust APIs that handle WhatsApp OTP delivery, intelligent multi-channel failover (e.g., trying WhatsApp first, then falling back to SMS or Voice), and native Viber business messaging.

Top providers offering WhatsApp and/or Viber OTP capabilities include:

1. Twilio Verify API
   • Channels: WhatsApp, SMS, RCS, Voice, Email.
   • Why use it: Twilio's Verify product abstracts the channel logic completely. You generate a single verification session, and Twilio orchestrates delivery across WhatsApp and other channels. It auto-creates localized Meta-approved authentication templates with "copy code" buttons.[twilio.com](https://www.twilio.com/docs/verify/whatsapp)
2. Infobip
   • Channels: WhatsApp, Viber, SMS, Voice.
   • Why use it: Infobip has extensive global carrier and OTT reach, making them very strong in regions where Viber is heavily favored (like Eastern Europe and parts of the Middle East/CIS) alongside deep WhatsApp Business platform support. They offer pay-per-successful-delivery models and automated SMS failover.[twilio.com](https://www.infobip.com/viber-business/otp)[[2](https://www.infobip.com/viber-business/otp)]()
3. Vonage Verify API
   • Channels: WhatsApp (including Zero-Tap/One-Tap autofill), SMS, Voice (TTS), Email.
   • Why use it: Vonage supports advanced workflow sequences, built-in conversion tracking, and anti-fraud protections (like AIT - Artificially Inflated Traffic protection), routing seamlessly between WhatsApp and fallback methods.[twilio.com](https://developer.vonage.com/en/verify/code-snippets/send-request-whatsapp-v2)[[2](https://www.infobip.com/viber-business/otp)](https://www.vonage.com/communications-apis/verify/)
4. LINK Mobility
   • Channels: Viber Business Messages, WhatsApp, SMS, Email.
   • Why use it: An official Rakuten Viber messaging partner with massive footprint coverage across Europe and international markets, specializing in direct enterprise connections for rich messaging apps.[twilio.com](https://www.forbusiness.viber.com/en/messaging-partners/)
5. Regional / Specialized CPaaS (e.g., MSG91)
   • Channels: WhatsApp, SMS, Voice.
   • Why use it: If you are dealing with specific regional delivery blocks or want direct developer-friendly access to template triggers without enterprise-tier minimum billing constraints.[twilio.com](https://msg91.com/help/whatsapp/whatsapp-otp)

Best Practices When Implementing:

• Failover Logic: Always configure a fallback channel. Not every user registered on a phone number actively uses WhatsApp or has Viber installed; if the app check fails or times out, the system should cleanly fallback to SMS or a Voice text-to-speech call.[twilio.com](https://www.vonage.com/communications-apis/verify/)[[2](https://www.infobip.com/viber-business/otp)](https://www.infobip.com/whatsapp-business/otp)
• Meta/Viber Templates: For WhatsApp specifically, you must use pre-approved Meta Authentication Templates which support automated copy-paste / one-tap autofill features to maintain a smooth user experience.[twilio.com](https://developers.facebook.com/documentation/business-messaging//templates/authentication-templates/authentication-templates)

If you'd like, let me know:

• Which specific countries or regions are failing for you
• Whether you prefer a fully managed verification API (like Twilio/Vonage) or building custom direct-provider templates

I can help you narrow down which provider has the best delivery rates or regional pricing for your target markets.

When SMS delivery fails due to carrier filtering, high costs, or poor local infrastructure in specific countries, switching to an alternative IP-based channel like WhatsApp or Viber is a reliable fix . Several major Communications Platform as a Service (CPaaS) providers offer robust APIs for multi-channel authentication.[sinch.com](https://sinch.com/verification-api/whatsapp-otp/)[[2](https://www.twilio.com/docs/verify/whatsapp)](https://www.twilio.com/docs/verify/whatsapp)

Top Providers for WhatsApp and Viber OTP Delivery

• Infobip
  • Channels: Supports both WhatsApp and Viber (via their dedicated Viber Business Messages API and Authenticate solution).
  • Best For: High-scale international authentication with massive direct operator connections, making them especially strong in Eastern Europe, parts of APAC, and regions where Viber is heavily favored.[sinch.com](https://www.infobip.com/viber-business/otp)[[2](https://www.twilio.com/docs/verify/whatsapp)](https://sms.to/blog/7-best-otp-api-providers-full-comparison-guide/)

Key Technical & Compliance Considerations

1. Pre-Approved Templates: For WhatsApp, you cannot just fire arbitrary text strings. You must submit and get pre-approved Authentication Templates (which include the code placeholder and optional expiration timers) via Meta/your provider.[sinch.com](https://www.techtonetworks.com/post/how-to-automate-otp-delivery-using-whatsapp-business-api-with-techto-networks)[[2](https://www.twilio.com/docs/verify/whatsapp)](https://sinch.com/verification-api/whatsapp-otp/)[[3](https://www.infobip.com/viber-business/otp)](https://.com/blog/how-to-send-otp-on-/)

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

• Which specific countries or regions are failing for you?
• Do you prefer a managed verification API (that handles the code generation and failover logic automatically) or a raw messaging API?

When SMS delivery fails or becomes too costly in specific regions (such as parts of Eastern Europe, APAC, or Latin America), routing OTPs through over-the-top (OTT) messaging apps like WhatsApp and Viber is an effective strategy.

Several major Communication Platform-as-a-Service (CPaaS) providers support multi-channel authentication with built-in fallbacks (e.g., trying WhatsApp/Viber first, then falling back to SMS or Voice if unreached):[twilio.com](https://www.twilio.com/docs/verify/whatsapp)[[2](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services)](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services/)

Major Providers Supporting WhatsApp & Viber OTP

1. Infobip

• Channels: WhatsApp, Viber, SMS, Voice, RCS.
• Details: Infobip has robust support for Viber OTP via their Authenticate solution or Viber Business Messages API, alongside comprehensive WhatsApp Business API integration. They excel in global coverage with direct operator connections and automated channel switching.[twilio.com](https://www.infobip.com/viber-business/otp)

2. Sinch

• Channels: WhatsApp, Viber, SMS, Voice.
• Details: Sinch offers a unified Conversation API and Verification API that supports predefined Viber Business Template Messages for OTP. They are heavily recommended if your problem regions are concentrated in Europe or require complex multi-channel fallback workflows.[twilio.com](https://developers.sinch.com/docs/conversation/channel-support/viberbm/template-support)[[2](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services)](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services/)

3. Twilio

• Channels: WhatsApp, SMS, RCS, Voice.
• Details: Twilio’s Verify WhatsApp API is built specifically for this use case. It intelligently orchestrates OTP delivery across channels, generating a single code and attempting delivery via WhatsApp first, with automated fallback to SMS or voice. (Note: Twilio supports Viber less natively out-of-the-box compared to Infobip or Sinch, usually requiring custom orchestration or alternate gateways for Viber). [twilio.com](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services/)[[2](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services)](https://www.twilio.com/docs/verify/whatsapp)

4. Gupshup

• Channels: WhatsApp, SMS, Voice.
• Details: Highly optimized for high-volume conversational and transactional messaging, particularly strong in India and parts of APAC where WhatsApp OTP adoption is exceptionally high.[twilio.com](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services/)

Key Considerations Before Switching

• Fallback Strategy: Look for an API that provides an automatic fallback chain (e.g., WhatsApp → Viber → SMS). If a user doesn't have WhatsApp installed or active, the system needs to seamlessly drop back to SMS so the user isn't locked out.
• Template Approvals: Both WhatsApp and Viber require pre-approved message templates for authentication codes. You cannot send free-form text as an OTP.[twilio.com](https://www.infobip.com/docs/viber/business-messages/message-templates/transactional)[[2](https://www.plivo.com/blog/whatsapp-api-providers-banking-financial-services)](https://developers.sinch.com/docs/conversation/channel-support/viberbm/template-support)
• Opt-in/Session Rules: Networks like Viber and WhatsApp enforce strict compliance regarding transactional message delivery and user initiation. Using a certified CPaaS provider ensures these template constraints and session handshakes are handled programmatically.

If you can share which specific countries or regions are giving you trouble, I can help you figure out which channel (WhatsApp vs. Viber) has the highest local penetration there.

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.Twilio+1

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.