WhatsApp Business API is the messaging channel with the highest engagement rates on the planet and also the one with the most footnotes. Templates, session windows, conversation-based pricing, tier limits, green ticks — there's a lot to keep straight. Here is what actually matters when you're picking WhatsApp for transactional messaging.
API, not app
The WhatsApp Business API is not the WhatsApp Business app. The app is fine for a corner shop. The API is what Zomato, Uber and your bank use to send you order updates, boarding passes and payment confirmations at scale. You access it through an official Business Solution Provider like OTP SMS.
You get a dedicated business phone number, a display name, and — if you're a real brand with real customers — a green verification tick. Users see your logo, your name, and they trust the conversation.
Templates and the 24-hour window
You cannot send whatever you want. Every business-initiated message must use a template pre-approved by Meta. Templates fall into three categories: authentication (OTPs, verifications), utility (order updates, appointment reminders, receipts) and marketing (promotions).
Once a user replies, a 24-hour 'session window' opens in which you can send free-form messages. This is where two-way support flows live. Miss the window and you're back to templates.
When WhatsApp beats SMS
WhatsApp shines for anything longer than a code. Order receipts with itemised lists, boarding passes with QR codes, appointment reminders with reschedule buttons — these live natively in WhatsApp and land with a familiar chime.
It also wins in countries where WhatsApp is the default messaging app: India, Brazil, Indonesia, most of the Middle East, most of Europe. For pure OTP traffic in the United States, SMS is still cheaper and more universal.
Pricing without the fog
Meta charges per conversation, not per message, in 24-hour buckets. Authentication conversations are the cheapest tier. Utility next. Marketing is the most expensive. On top of Meta's price, your BSP charges a per-message platform fee. At OTP SMS we publish both numbers on one line. Ask any provider who doesn't.
The WhatsApp Business API is powerful, but it's also opinionated. Learn the rules once, and it becomes the highest-engagement channel in your stack. Skip the homework, and Meta will quietly rate-limit you into oblivion.
