Quick answer: On the WhatsApp Business API, a customer service window is a 24-hour timer that opens when a customer messages or calls your business. While it is open you can reply with ordinary, non-template messages. When it closes, you can only send approved message templates. A new message from the customer opens a fresh window.
This one rule shapes almost every WhatsApp conversation flow, support bots and reminders included. It is also the rule most often misunderstood by teams that move from the WhatsApp Business app to the API. If you are starting from scratch, read our guide to what the WhatsApp Business API is and how it works in India first.
What opens the window
The customer starts it. Meta's pricing documentation describes the window as a 24-hour timer that opens when a user messages or calls the business. Nothing you send can open it. If a customer has not written to you, you have no window, and the first message has to be a template.
Each new message from the customer restarts the 24 hours. A customer who replies at 10 in the morning and again at 8 in the evening keeps the conversation open past the first day.
What you can send inside the window
Inside the window you can send non-template replies, which Meta's pricing page calls service messages. That means free text, images, documents, buttons and lists as the conversation needs. You are answering a question the customer asked, so you do not need a pre-approved format.
This is why chatbots and live agents work well on WhatsApp: the customer writes, and the business answers inside the window. Our guide on how AI chatbots improve customer support on WhatsApp shows what that looks like in practice.
What happens when the window closes
After 24 hours without a message from the customer, the window closes. You can still contact them, but only with an approved template, and only if you have their permission. Templates have to be created and approved in advance. Our guide to WhatsApp message templates explains categories and approval, and our guide to WhatsApp opt-in rules covers permission.
Practical patterns
- Answer fast. If a customer asks something at 6 pm and gets an answer at 6 pm the next day, you may be answering after the window has closed.
- Finish the job inside the window. If a support chat is likely to need more steps, close it out before the 24 hours run down, or ask the customer to confirm they are done.
- Use a template to restart. If you need to reach someone after the window closes, send a template with a clear reason, such as an update on their request.
- Do not rely on the window for campaigns. A campaign goes to people who have not just messaged you, so it uses templates.
Windows opened from ads
Meta's pricing page describes a longer window for conversations that start from a click-to-WhatsApp ad. If a user messages from such an ad and you reply within the window, the window stays open for up to seven days, and Meta's page lists marketing, utility, authentication and service messages as free during that period. Check the page for the current terms, because Meta updates them.
Window and cost
Under Meta's per-message pricing, which replaced conversation-based pricing on 1 July 2025, you pay for delivered messages by category and by the country of the recipient. As we read Meta's pricing page on 2 November 2026, each business phone number has a free allowance of 1,000 service messages a month, and charging for utility templates sent inside an open window began on 1 October 2026. Prices and free allowances change on set quarter dates, so check Meta's page before budgeting. Our guide to WhatsApp Business API pricing in India explains how the pieces fit.
How to check whether a window is open
Your platform or provider usually shows it. Many conversation tools display a countdown, or block free-text replies once the window closes. If you build on the API directly, your code can store the time of the customer's last message and compare it with the current time. The webhook that reports incoming messages carries that information; see our guide to WhatsApp API webhooks.
Our WhatsApp API and chatbot service is built around this flow: the customer starts, the bot or agent replies, and templates cover everything else.
Frequently asked questions
Can I message a customer who has not messaged me?
Only with an approved template, and only if the customer has given permission. There is no window until they write first.
Does every customer message reset the 24 hours?
Yes. The window runs from the customer's latest message or call.
Can I send a template while the window is open?
Yes. Templates can be sent at any time. The window only decides whether free-text replies are allowed.
What is a service message?
In Meta's pricing documentation, a service message is a non-template reply sent inside the 24-hour customer service window.
Is the window the same for every business?
The basic 24-hour rule applies to all. Windows that start from click-to-WhatsApp ads can last longer.
Sources checked
- Meta for Developers, WhatsApp Business Platform pricing page: the definition of the customer service window, service messages, the click-to-WhatsApp window and the 1,000 free service message allowance, read 2 November 2026. The page does not carry a last-updated date.
- Meta's pricing details change on set quarter dates. Check the page for current terms.
More in WhatsApp Business API guides.
Written by Rohit Jadhav. Last reviewed 2 November 2026.