Sending OTPs and Authentication Messages on WhatsApp

One-time passwords and login codes are how you verify a customer is who they say they are. Many businesses are moving these from SMS to WhatsApp — and for good reason. WhatsApp authentication messages are a distinct category with their own rules.

Here's how WhatsApp OTPs work and how to set them up.

What authentication messages are

Authentication is one of WhatsApp's four message categories, alongside Utility, Marketing and Service. These are the verification codes you send when a customer logs in, signs up, resets a password or confirms a sensitive action.

They use dedicated authentication templates and are priced in their own category. Because they're tied to a specific security action the customer initiated, they're high-trust and high-deliverability.

Why WhatsApp over SMS

Businesses move OTPs to WhatsApp for a few reasons: it reaches customers on an app they trust, the message carries your verified business identity rather than a random shortcode, and in many markets it's more reliable than SMS routing.

It also keeps the verification in the same channel the customer uses for everything else with you, which feels more cohesive than bouncing to SMS. Coupling and copy-code buttons make entering the code one tap.

How the flow works

The pattern is simple: your app generates a code, requests an authentication template send via the API with that code as a variable, and WhatsApp delivers it to the customer. They tap to copy or autofill, enter it, and you verify it on your side.

The code generation and verification stay in your system; WhatsApp is just the secure delivery channel. With a provider handling the API, the send is a single integrated step.

Setting it up

You'll need a WhatsApp Business API connection and an approved authentication template. Authentication templates have a specific format Meta expects — keep them strictly to the verification purpose, with the code as a variable and no marketing content.

Once the template is approved, connect it to your login or signup flow. With Defuser's WhatsApp Business API and integrations like Zapier or Make, you can trigger OTP sends from your existing systems without heavy custom work.

Best practices

Keep authentication messages purely functional — no upsells, no promos, or you risk rejection and recategorization. Make sure codes expire and aren't reused. Provide an SMS or email fallback for customers who aren't on WhatsApp.

And monitor delivery: because these are time-sensitive, a delayed code is a frustrated customer. The dedicated category and clean templates keep authentication fast and reliable.