- A customer must agree (opt in) before your business messages them on WhatsApp.
- After a customer writes to you, you can reply freely for 24 hours. After that you need an approved template.
- Keep the assistant about your business, tell customers it is automated, and always offer a person.
A dental clinic collects phone numbers on its booking form. One Monday, the manager sends everyone on the list a WhatsApp message about a new whitening offer.
By Wednesday, some patients have blocked the number. Messages stop arriving. Nobody at the clinic knows why.
The clinic broke a rule it had never heard of. WhatsApp has a few simple rules for businesses, and they are easy to follow once you know them. We build to these rules in our WhatsApp chatbot service.
Meta, the company behind WhatsApp, updates its rules from time to time. This guide explains the main ideas. Check the official pages under Sources before you launch.
What is the difference between the WhatsApp Business app and the API?
There are two ways for a business to use WhatsApp.
The WhatsApp Business app is the free app on your phone. You type the replies yourself. It suits a very small team.
The WhatsApp Business Platform is often called “the API”. An API is a way for two pieces of software to talk to each other. It lets a system send and receive WhatsApp messages for you, so automation becomes possible.
The rules below matter most when you use the API.
Rule 1: the customer must opt in
Opt-in means the customer has agreed to receive messages from your business. Meta asks that the opt-in makes clear the person is agreeing to messages from your business, by name. It doesn’t have to mention WhatsApp, but naming the channel is clearer for customers.
A phone number on an old invoice is not opt-in. A tick box that says “Yes, [your business name] can send me appointment reminders on WhatsApp” is.
Good ways to collect it:
- A clear tick box on your booking form
- A button on your website that opens a WhatsApp chat, so the customer writes first
- A QR code at the front desk that starts a chat
It also helps to say what you will send. “Reminders about your appointment” is clear. “Updates” is not.
Rule 2: what is the 24-hour window?
When a customer sends you a message, a 24-hour clock starts. Meta calls this the customer service window.
Inside the window, you can reply freely. Normal sentences, questions, a booking link.
Each new message from the customer restarts the clock.
When 24 hours pass with no message from the customer, the window closes. You can’t send a free-form message any more.
This is why speed matters on WhatsApp. If you answer inside the window, the conversation flows. We cover reply speed in how fast you should reply to a new lead.
Rule 3: when do you need a message template?
Outside the window, you can only send a template. A template is a message you write in advance and Meta approves.
A reminder template might read:
Hi {{name}}, this is a reminder of your appointment on {{date}} at {{time}}. Reply 1 to confirm or 2 to change it.
The parts in brackets are filled in for each customer.
Templates are for useful, expected messages: reminders, confirmations, updates the customer asked for. Marketing templates exist too, but customers can block and report them. Too many reports can limit your number.
| Situation | What you can send |
|---|---|
| Customer wrote to you in the last 24 hours | Any normal reply |
| More than 24 hours since their last message | An approved template only |
| Customer never opted in | Nothing. Get opt-in first |
What does the WhatsApp Business API cost?
The WhatsApp Business app is free.
On the API, Meta charges per delivered message. The rate depends on the message category, such as marketing, utility or authentication, and on the customer’s country. Some messages are free or have a free allowance, and conversations that start from a click-to-WhatsApp ad get a free period. Rates and free allowances change, so we don’t quote them here. Meta’s own pricing page is linked under Sources.
Keep the assistant about your business
Since 15 January 2026, Meta’s terms for the WhatsApp Business Platform don’t allow general-purpose AI chatbots, where the AI assistant itself is the product. An assistant that serves your own customers, for bookings or support, is a different case.
That fits a small business well. Your assistant should answer about your hours, your services and your bookings. It should not try to chat about everything.
Three habits keep you safe:
- Say it is automated. The first message should make that clear.
- Offer a person. “Reply HUMAN to talk to our team.”
- Stay inside approved answers. If the assistant doesn’t know, it hands over.
WhatsApp’s policy also says that when you use automation, customers need a quick, clear way to reach a person. Meta can update these rules at any time, so review them when it announces changes.
Step by step: a setup that follows the rules
- Decide what the assistant will handle. Start small: opening hours, prices you already publish, bookings.
- Add opt-in to every place you collect a number.
- Write your templates for reminders and confirmations, and send them to Meta for approval.
- Build the flow. n8n, a tool that connects your apps and runs steps automatically, receives each message. Claude, an AI model, writes the reply from your approved information.
- Add the hand-off. A person is told as soon as a customer asks for one.
- Test with real phones before any customer sees it.
Automation recipe: a WhatsApp booking assistant that follows the rules
- When this happensA customer sends your business a WhatsApp message.
- The system doesThe system notes the time, because the 24-hour window starts now.
- ThenClaude answers from the information you approved, and says it is an automated assistant.
- ThenIt offers free slots from your calendar and books the one the customer picks.
- ThenA reminder template goes out the day before, only to customers who opted in.
- You onlyTake over when the customer asks for a person, or when the question is outside the approved answers.
- WhatsApp Cloud API
- n8n
- Claude
- Google Calendar
- Google Sheets
Common mistakes
Treating a phone list as permission. This is the clinic’s mistake from the start of this guide.
Sending marketing to everyone. Send fewer, more useful messages. A reminder helps. A weekly offer gets blocked.
No way to reach a person. People get stuck, then they get angry.
Vague templates. Meta can reject them. Write exactly what the message is for.
Ignoring the window. If your team replies the next afternoon, the window has closed and the reply won’t send.
A simple next step
Open your booking form today. If it has no WhatsApp tick box, add one. That single change makes everything else possible.
WhatsApp is one of ten jobs worth handing over first. The full list is in 10 tasks a small business can automate this month.
Want a second pair of eyes on your setup? Book a free video call and I’ll walk through it with you.
Sources
- Meta: getting opt-in for WhatsApp
- Meta: WhatsApp Business Platform pricing
- WhatsApp Business Messaging Policy
- Meta Terms for WhatsApp Business Platform
This guide was drafted with AI assistance, then reviewed, fact-checked and edited by MD Al Amin.
Quick questions
Can I message customers who gave me their phone number?
Not for that reason alone. Having a number is not the same as opt-in. The customer needs to agree to receive messages from your business, and it should be clear what they are agreeing to.
What happens when the 24 hours run out?
You can no longer send a free-form message. You can send an approved template, and if the customer replies, a new 24-hour window opens.
Is the free WhatsApp Business app enough for me?
For a small business with one phone and a few chats a day, often yes. You need the API (the WhatsApp Business Platform) when you want automation, several team members or a connection to your other tools.