The WhatsApp 24-hour window: a guide to the official API for selling without stalling your follow-up

Anyone who moves their sales operation from the WhatsApp Business app to the official API tends to trip over the same thing. The salesperson wants to send "hey, did you get a chance to look at the proposal?" to a lead who went quiet two days ago, and the system won't let them. It's not a bug. It's the 24-hour window.

Understanding this rule is what separates a WhatsApp operation that scales from one that keeps fighting the tool. This guide explains the customer service window, templates, message categories, number quality and, above all, what all of this changes in the design of your follow-up.

What is the 24-hour window

On the official WhatsApp API (Meta's WhatsApp Business Platform), every conversation has a customer service window. It opens when the customer sends a message to your business and lasts 24 hours from their last message.

• Inside the window, you can send free-form messages: text, audio, images, documents, written on the spot, by a human or by an AI agent.
• Outside the window, you can only start contact with a template: a message pre-approved by Meta, with variables you fill in.

Every time the customer replies, the window resets for another 24 hours. That's why an active conversation never runs into the rule, and a conversation that has gone cold always does.

Why Meta does this

The rule exists to protect users from spam. Meta wants businesses to speak freely only with people who are actually in a conversation with them. For everything else, the content goes through approval and sending is charged. In practice, this keeps WhatsApp a channel where people still read messages from businesses, which is good for anyone who plays by the rules.

What are WhatsApp templates

Templates are message models you register, Meta reviews and, once approved, can be sent at any time to anyone who has given consent. They support variables (name, product, date), quick-reply buttons and calls to action.

Each template belongs to a category:

Two precautions that save headaches:

• Don't try to pass marketing off as utility. Meta reviews the category and may reclassify the template. Sales follow-up to a lead who hasn't bought yet is marketing.
• Write templates that work as conversation openers. The goal of a template is not to sell. It's to get the person to reply, because the reply reopens the window and brings the conversation back to free-form territory.

How pricing works

Since July 2025, Meta charges per delivered template, with prices that vary by category and country. Free-form messages inside the customer service window are not charged, and neither are utility templates sent while the window is open. Conversations that start from a click-to-WhatsApp ad open a free 72-hour window. The rates change fairly often, so check Meta's current price table before projecting the cost of a campaign.

Number quality and messaging limits

Every number on the API has a quality rating, calculated from how recipients react to your messages: blocks, reports and silence count against you. Quality affects how many new people you can contact per day. The limit grows as you send volume that is well received, and it can be lowered if quality drops.

What keeps quality high:

• Messaging only people who have given consent.
• Segmenting: the same message to everyone is a recipe for getting blocked.
• Always offering an easy way out ("if this no longer makes sense, just let me know").
• Stopping the cadence when the person asks, and recording it.

What the window changes in your follow-up

Here is the practical consequence most companies only discover after migrating: you need two different follow-up cadences, not one.

Campaign cadence: for people who never replied

You sent the opening template and the person didn't reply. There is no open window. Every subsequent attempt also has to be an approved template. This cadence is short, spaced out in days, and each message needs to give a new reason to reply.

Conversation cadence: for people who replied and went quiet

The person replied, chatted a bit and stopped. The window is open, so the first follow-ups can be free-form messages, written from the context of the conversation: "Gui, any questions about the time I sent you?". When the window closes, the cadence switches to templates.

An example timeline:

It's also worth having a specific cadence for sensitive stages, such as proposal sent, with its own tone and intervals. We put together complete templates in the article on WhatsApp follow-up cadences.

Scheduled messages and the window

Scheduling messages has a catch. If you schedule a free-form text for tomorrow at 6 p.m. but the window closes today at 8 p.m., the message can't go out as free-form text. A good tool checks this at scheduling time and asks for a template when the chosen time falls outside the window.

Well-designed AI agents handle this differently: instead of scheduling the finished message, they schedule the intent to follow up. At the scheduled time, they reassess: does it still make sense to contact this person? Did someone add a note, did the lead send a message, did the deal change stage? If it makes sense, they pick the right format: free-form text if the window is open, the most suitable template if it's closed.

Common pitfalls when setting up the number

Some problems show up in almost every official API project:

• A business portfolio with no owner. The number has to sit in a Meta Business portfolio. If the company's portfolio was created by someone who left, or is tied to an email nobody can access, verification gets stuck. Sometimes it's faster to create a new portfolio, with an email the company controls, just for WhatsApp.
• Two systems trying to send from the same number. In practice, each number is operated by a single provider on the API. If your CRM or marketing tool already sends from the number and you want another system to hold conversations on it, the right design is to pick one orchestrator: the CRM decides when to send and calls the system connected to WhatsApp to deliver it.
• Fear of losing history when migrating. Coexistence is now available: the same number can stay in the WhatsApp Business app on the phone and, at the same time, be connected to the API. The salesperson keeps the same phone and the same conversation, and the company gains records, integration and governance.

Official API or unofficial API?

Tools that connect WhatsApp by scanning a QR code, without going through Meta's API, exist and are cheap. So does the risk: the number can be banned without warning, taking the history and the customer relationships with it. For a sales operation that depends on the channel, the official API is the only sustainable path. Sailer is an official Meta partner and operates exclusively on the official API.

Frequently asked questions

Can I send a free-form message to a customer who talked to me yesterday?

If more than 24 hours have passed since their last message, no. You need to use a template. When they reply, the window reopens.

Does a template have to be approved every time I change the customer's name?

No. You approve the model with variables, and the variables are filled in on each send.

How long does template approval take?

It's usually fast, from minutes to a few hours, when the text follows the policies and the category is correct.

Do messages sent by an AI agent follow the same rules?

Yes. Meta doesn't care whether a human or an AI wrote the message. Inside the window, free-form. Outside it, template.