Short answer
Most businesses should send OTP codes by both SMS and WhatsApp rather than choosing one. WhatsApp authentication templates offer one-tap, zero-tap and copy-code autofill and are delivered only to the user's primary WhatsApp device, but reach only WhatsApp users. SMS reaches almost every phone. A common pattern is WhatsApp first, SMS fallback.
SMS OTP vs WhatsApp OTP
| Factor | SMS OTP | WhatsApp OTP |
|---|---|---|
| Reach | Almost every mobile phone | Users with WhatsApp installed |
| Autofill | Android SMS Retriever API; iOS suggests codes from SMS | One-tap, zero-tap and copy-code buttons; iOS 26 keyboard suggestions |
| Sender | Registered sender ID | Business profile on WhatsApp |
| Pricing | Per message by destination and route | Per delivered authentication message, by recipient market |
| Setup | Sender ID registration where required | Approved authentication template |
When WhatsApp is the better first channel
WhatsApp suits markets where most users already have it and your app runs on Android, where one-tap and zero-tap autofill remove manual typing. Meta charges authentication messages per delivered message by recipient market, and some markets have a separate authentication-international rate, so check Meta's pricing page before routing cross-border traffic.
SMS is the safer default for first sign-up, users without WhatsApp, and markets where WhatsApp is restricted.
How to set up OTP with fallback
OmniChannels.ai sends OTPs over WhatsApp authentication templates (one-tap, zero-tap and copy-code), SMS and voice, with channel fallback configured per use case.
- Tell the user which channel the code will arrive on.
- Send a WhatsApp authentication template to WhatsApp users.
- If it is not delivered within a short timeout, send the same code by SMS.
- Offer a voice call as a last option for landlines and accessibility.
- Rate-limit requests and track codes entered per channel.