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 too costly in certain regions (such as parts of Eastern Europe or Asia for Viber , or globally for WhatsApp), using a CPaaS (Communications Platform as a Service) provider with multi-channel fallback is the standard solution.

Several major communication API providers support OTP delivery over WhatsApp and Viber (frequently packaged with automated SMS, voice, or RCS fallback):

• Infobip - Offers Infobip Authenticate , a robust omnichannel solution supporting SMS, WhatsApp, Viber, RCS, and voice. It handles high-scale international authentication with built-in template management for secure, branded messaging.
• Vonage - Vonage Verify API supports multi-factor authentication routing across SMS, WhatsApp, Viber, voice, and email, alongside anti-fraud features.
• Twilio - Twilio Verify supports WhatsApp as a delivery channel alongside traditional SMS and voice. It also includes automatic fallback features from WhatsApp to SMS if a message fails or a region lacks coverage.
• Dexatel - Provides a dedicated Viber OTP and multi-channel verification tool with high deliverability spanning a wide global footprint.
• Prelude - A modern verification API provider featuring multi-routing across 50+ providers and channels including WhatsApp, Viber, RCS, and Telegram, specifically built to optimize costs and conversion rates in regions where SMS underperforms.

Note: To send OTPs via WhatsApp, Meta requires you to use pre-approved Authentication Templates (which feature structure constraints like a code placeholder and an optional copy-code/one-tap button).

If you can share which specific countries or regions you are having trouble with, I can help you figure out which of these providers has the strongest local delivery routes for WhatsApp and Viber there.

Yes. There are several CPaaS/authentication providers that can deliver OTPs over WhatsApp, and some also support Viber.

My shortlist

1. Infobip — probably the best match for your problem.
Its Authenticate product provides a single API supporting SMS, WhatsApp, Viber, RCS and other channels, with routing/failover between channels. That means you can retain your existing SMS flow and route OTPs through WhatsApp or Viber when appropriate.

2. Sinch — particularly attractive if you want a verification-focused API.
Sinch's Verification API explicitly supports WhatsApp alongside SMS, flash calls, voice and data verification. Its Conversation API also supports Viber Business and WhatsApp, so you can build broader channel fallback if needed.

3. Vonage — good if WhatsApp is your primary alternative to SMS.
Vonage Verify supports SMS, RCS, WhatsApp, voice, email and Silent Authentication. Its WhatsApp verification flow supports both standard OTP and Android zero-tap verification.

One important caveat

Don't assume that "supports WhatsApp/Viber" means equal coverage in every country. For your particular problem, I'd evaluate providers on a country × carrier × channel basis—especially whether WhatsApp/Viber is available to the recipient, whether authentication templates are permitted, local sender requirements, delivery rates, and pricing.

If you give me the countries where SMS is failing, I can compare these providers specifically for those countries and identify which one has the strongest WhatsApp/Viber coverage.

When SMS delivery fails or is unreliable in specific regions, switching to chat-app-based OTP delivery via WhatsApp or Viber is a standard industry workaround. Several major CPaaS (Communications Platform as a Service) providers and verification APIs support these channels, often featuring intelligent multi-channel fallback (e.g., trying WhatsApp/Viber first, then falling back to SMS or Voice if the chat message cannot be delivered).

Top providers offering WhatsApp and/or Viber for OTP delivery include:

• Infobip : Extensive global reach with dedicated Viber OTP and WhatsApp Business API integrations, featuring built-in SMS/voice failover workflows.
• Twilio Verify API : Supports WhatsApp as a native verification channel alongside SMS, email, and voice. It includes automatic failover options from WhatsApp to SMS and pre-approved Meta authentication templates.
• Vonage Verify API : Offers multi-channel workflows including WhatsApp (with standard OTP or Android "zero-tap" auto-fill options) and supports overarching fallback routing.
• Dexatel : Specializes in rich messaging channels including Viber OTP with high delivery rates across Eastern Europe, Southeast Asia, and the Middle East, plus automatic fallback to SMS.
• Telnyx Verify API : Provides programmatic verification via WhatsApp with behind-the-scenes template management and webhook-driven SMS fallback capabilities.
• SMS.to : Offers a unified Verify API routing messages across WhatsApp, Viber, Telegram, and SMS with customizable fallback logic.

Note: To send OTPs via WhatsApp, Meta requires you to use pre-approved Authentication Templates (which restrict the format to include the code safely with copy/autofill buttons).

If you share which specific countries or geographic regions are giving you trouble, I can help you see which provider has the strongest local delivery rates for WhatsApp versus Viber.

Yes. If SMS OTP is unreliable in particular countries, there are several providers worth evaluating for WhatsApp and/or Viber OTP, especially those that can fail over between channels.

The strongest candidates if you specifically need both WhatsApp and Viber are Infobip, Sinch, Telesign, Dexatel, SMS.to, and Verigator. Current provider information indicates that SMS.to's Verify API, for example, can send through SMS, Viber, WhatsApp, or voice and automatically fall back when the primary channel fails.

A particularly important point is country-by-country coverage. Viber is disproportionately useful in parts of Eastern Europe/CIS and some MENA markets, so don't select a provider solely based on its global channel list. Viber itself supports authentication/verification traffic through Business Messages, and its 2026 updates include OTP auto-copy functionality.

What I'd shortlist

• Infobip — probably my first enterprise evaluation if you need WhatsApp + Viber + SMS with intelligent routing.
• Sinch — strong alternative for global-scale authentication.
• Dexatel — attractive if you want an API specifically oriented around multi-channel OTP/fallback.
• SMS.to — worth testing if you want a relatively simple Verify API and explicit channel failover.
• Twilio — excellent if WhatsApp + SMS is sufficient and you already use Twilio; it doesn't solve the Viber requirement.

You can also integrate WhatsApp directly through Meta's official WhatsApp Business Platform, including authentication templates/OTP functionality, rather than going through a CPaaS provider.

If you tell me the countries where SMS is failing and roughly how many OTPs/month you send, I can narrow this to 2–3 providers and compare their country coverage, fallback behavior, pricing, and integration effort.

To bypass unreliable SMS delivery routing in specific international regions, enterprise applications leverage Communications Platform as a Service (CPaaS) providers that integrate over-the-top (OTT) messaging APIs. Infobip, 8x8, Sinch, and Vonage are the primary global vendors supporting both WhatsApp and Viber for secure, programmatic one-time password (OTP) delivery.

Top CPaaS Providers for WhatsApp and Viber OTP

• Infobip : Features native, carrier-approved connectivity for Viber OTP alongside comprehensive WhatsApp Business API integration , enabling automatic multi-channel fallback if a user is unreachable on one platform.
• 8x8 CPaaS : Offers a unified Verification API supporting SMS, WhatsApp, and Viber Business messaging with smart fallback routing to maximize delivery rates.
• Sinch : Delivers robust enterprise-grade verification tools that incorporate global messaging channels, including WhatsApp and Viber, tailored for high-volume cross-border authentication.
• Vonage (Ericsson) : Provides programmable Vonage Verify API endpoints that route authentication codes dynamically across multiple channels like WhatsApp, SMS, and voice.
• Twilio : Manages a versatile Twilio Verify API that natively supports WhatsApp and voice fallback, though native Viber routing is typically left to specialized regional providers like Infobip.

If you can share the specific countries or geographic regions where your SMS failures are happening, I can help determine whether WhatsApp, Viber, or another fallback channel has higher local adoption there.

Yes. If you’re looking for OTP/verification providers that can use WhatsApp or Viber when SMS is unreliable, the strongest options I’d investigate are:

1. Infobip — probably the closest match

Infobip offers a dedicated Authenticate product supporting SMS, WhatsApp, Viber, RCS and other channels through one integration. It also supports routing/failover, so you can use WhatsApp or Viber where SMS performs poorly.

For your use case, I'd specifically ask them about country-level channel availability and automatic SMS → WhatsApp/Viber fallback, because availability and commercial terms vary by destination.

2. Sinch

Sinch has a WhatsApp OTP offering through its Verification/Conversation APIs. It is particularly relevant if WhatsApp is your primary alternative to SMS.

3. Dexatel

Dexatel is another provider worth evaluating if you specifically need a broader set of OTP channels, including WhatsApp and Viber. I'd validate its coverage and deliverability directly against your affected countries before committing.

One important distinction

WhatsApp OTP isn't simply an SMS API with a different destination. You generally need an approved WhatsApp Business setup/authentication template and must comply with WhatsApp's requirements. Infobip, for example, explicitly supports authentication templates and WhatsApp-specific OTP flows.

If you give me the specific countries where SMS is failing, I can compare Infobip vs. Sinch vs. other providers by country, supported channel (WhatsApp/Viber), API, pricing model, and fallback capabilities.

If you're looking to supplement SMS OTP delivery in countries where SMS is unreliable, several communications platforms (CPaaS) support WhatsApp for authentication, and a smaller group also support Viber.

Recommendations

• If you primarily need WhatsApp OTP: Twilio, Infobip, Sinch, Plivo, and Vonage are all solid choices.
• If you specifically need Viber OTP: Infobip, Sinch, Vonage, Telesign, and Dexatel are the strongest options.
• If you want automatic failover: Look for providers that can route across channels (e.g., WhatsApp → SMS → voice) instead of requiring you to build the logic yourself. Twilio offers this for some Verify deployments, while providers such as Infobip, Telesign, and Dexatel emphasize built-in omnichannel routing.

A few implementation considerations:

• WhatsApp authentication requires onboarding with the WhatsApp Business Platform, so setup is typically more involved than SMS.
• Viber has strong penetration in parts of Eastern Europe, the Balkans, and some CIS countries, but is much less common elsewhere. Choosing channels based on user adoption by country generally yields the best delivery rates.
• Many teams offer multiple verification methods (SMS, WhatsApp, voice, email, TOTP/passkeys) and dynamically select the best one based on the destination country and recent delivery performance.

If you can share which countries are experiencing SMS failures and your approximate monthly OTP volume, I can narrow this down to the providers that typically perform best in those regions.

When SMS delivery fails or becomes too expensive in specific regions (such as parts of Eastern Europe, Southeast Asia, or Latin America), switching to an omnichannel verification API that supports WhatsApp and Viber is a reliable workaround.

Major CPaaS (Communications Platform as a Service) providers offer unified Verify APIs with built-in failover logic—meaning the system can try WhatsApp or Viber first, and fall back to SMS or Voice if the user isn't active on those apps.

Top providers supporting WhatsApp and/or Viber OTP delivery include:

• Infobip : Excellent for high-scale international authentication. It natively supports both Infobip WhatsApp Business API and Infobip Viber Business Messages for OTP with smart omnichannel routing and templates.
• Vonage : Their Vonage Verify API supports multi-channel workflows including SMS, Voice, and WhatsApp (complete with "Zero-Tap" auto-verification for Android users).
• Twilio: Twilio Verify API handles programmatic switching across SMS, Voice, Email, and Twilio WhatsApp API seamlessly within a single verification request.
• Sinch : Provides enterprise global verification and conversation APIs that support SMS, Voice, WhatsApp, and Sinch Viber Business Messages.
• CM.com : Offers global messaging APIs with integrated support for CM.com Viber Business Messaging and WhatsApp channels.

If you share which specific countries or regions are failing for your SMS traffic, I can help you figure out whether WhatsApp or Viber has higher local penetration there to optimize your routing.

Several major CPaaS (Communications Platform-as-a-Service) and enterprise API providers support WhatsApp and/or Viber for OTP and multi-factor authentication (MFA) delivery. Many of these platforms feature unified "Verify" APIs that automatically handle formatting, templates, and fallback logic (such as failing over to SMS or voice if the app-based message isn't delivered).

Top providers offering WhatsApp and Viber OTP delivery include:

• Infobip: Exceptional global footprint with robust, native multi-channel orchestration. Infobip supports dedicated Viber OTP template messages alongside WhatsApp, SMS, and RCS, making it very strong for regions where Viber and WhatsApp dominate. They also provide automated fallback scenarios (e.g., trying Viber/WhatsApp first, then falling back to SMS).
• Twilio: Through its Twilio Verify API , Twilio allows you to switch or cascade verification channels (SMS, WhatsApp, Voice) with minimal code changes. It has broad international coverage and manages backend rate-limiting and code generation.
• Vonage (Nexmo): Provides a comprehensive Messages and Verify API supporting WhatsApp and Viber integration alongside standard SMS. They have a strong enterprise presence, particularly in Europe and parts of APAC/LATAM.
• Sinch: Offers an enterprise-grade Verification API that routes OTPs over multiple channels including WhatsApp. Sinch handles global carrier connections and high-volume transactional messaging.
• Telnyx: Features a unified Verify API that supports WhatsApp alongside SMS and Voice with built-in failover capabilities and competitive, transparent pricing.
• Bird (formerly MessageBird): Omnichannel cloud communications platform that supports WhatsApp Business API and alternative social channels for authentication flows, with a strong footprint in Europe and international markets.

Key Implementation Considerations:

1. Meta/WhatsApp Requirements: To send WhatsApp OTPs, you must use pre-approved Authentication Templates via the WhatsApp Business API and complete Meta Business Verification.
2. Viber Requirements: Viber requires pre-registered and approved Viber OTP templates through their business messaging framework.
3. Automatic Fallback: Look for providers that offer an omnichannel fallback strategy (e.g., trying WhatsApp/Viber -> if unread/undelivered within X seconds -> fallback to SMS or Voice) to maximize your verification success rate.

If you can share the specific countries giving you trouble or your current primary API provider , I can help narrow down which of these platforms has the best direct routing or failover for those regions.

If SMS OTP delivery is unreliable in some countries, several communications platforms (CPaaS) support WhatsApp as an authentication channel, and a smaller number also support Viber. The strongest options are:

If Viber is important

Your shortlist is much smaller. The best-known providers with native Viber verification support are:

These platforms can generally attempt delivery over WhatsApp or Viber first and automatically fall back to SMS or voice if the preferred channel isn't available.

Things to consider

• User reach: WhatsApp has much broader global adoption than Viber, though Viber remains particularly strong in parts of Eastern Europe, the Balkans, and some Asian markets.
• Fallback logic: Look for configurable channel routing (e.g., WhatsApp → SMS → Voice) rather than implementing retries yourself.
• Compliance: WhatsApp OTPs require approved message templates and a WhatsApp Business account through Meta or a Business Solution Provider.
• Pricing: WhatsApp pricing differs from SMS and varies by country and message category, so compare your highest-volume destinations.

If you're primarily trying to improve OTP success rates in markets where SMS is unreliable, a provider such as Telesign, Infobip, or Sinch offers the broadest multi-channel verification capabilities. If you specifically need both WhatsApp and Viber with flexible routing and a developer-friendly API, Dexatel is another option to evaluate.