The WhatsApp 24-hour customer service window, precisely

The window opens when the customer messages you, and it runs for 24 hours from their last message. Inside it you can reply in your own words, with nobody approving the wording first. That is a permission about format, not an exemption from the rules about content: the Business Messaging Policy applies to what you send inside the window exactly as it does outside it. Outside the window you cannot send wording of your own at all, only a message Meta approved in advance. That one rule decides what any WhatsApp reply tool can and cannot do.

What opens it, and what resets it

Meta’s Service messages page, updated May 21, 2026 and read by us on 19 September 2026, states the mechanism in two sentences:

When a WhatsApp user messages you or calls you, a 24-hour timer called a customer service window starts. If the user messages or calls you again before the timer expires, the timer resets to 24 hours.

Two things in there carry weight. A voice call counts: Meta names messages and calls as equally window-opening. And the clock is not a session. It runs from the customer’s most recent inbound and resets in full every time they come back, so a conversation spread over three days never has a closed window in it.

WhatsApp’s Business Messaging Policy says the same in contract language, and adds a detail the developer page does not:

You may reply to a user message without use of a Message Template as long as it’s within 24 hours of the last user message. Conversations initiated by users open once the first business reply message is delivered. Outside the 24-hour customer service window, you may only send messages via approved Message Templates.

What you may send inside it

Meta’s name for what you send inside the window is a service message:

Service messages are free-form messages that you can send to WhatsApp users during a customer service window.

Free-form is the operative word, and Meta spells out the consequence on the same page: “service messages do not require pre-approval”. You compose the reply at the moment you send it, and nobody reviews it first.

Nobody reviewing it first is not the same as nothing governing it. The Business Messaging Policy is a single document that does not carve the window out of itself, and two of its requirements land squarely on what you type inside one. The content rule: “Do not confuse, deceive, defraud, mislead, spam, or surprise people with your communications.” And the rule aimed at automated replies specifically:

You may use automation when responding during the 24-hour window, but must also have available prompt, clear, and direct escalation paths.

So the window decides whether Meta pre-approves your wording. It does not decide whether the wording is allowed.

The page enumerates the permitted types: text, image, audio, video, document, sticker, contacts, location, location request, reaction, and the interactive reply button, list, call-to-action URL and Flow messages. Close to everything WhatsApp can render.

Two constraints come with it. The first is the delivery route:

Service messages can only be sent via the Messages API. To message WhatsApp users outside of a customer service window, use template messages instead.

The second is a caveat Meta publishes about its own platform, under a heading it labels a known issue:

In rare cases, you may receive a message from a WhatsApp user but be unable to respond within the customer service window.

We have not measured how often that happens and Meta publishes no figure for it. It is here because a reply that fails this way is not a bug in your tool.

What you must use a template for outside it

From Meta’s pricing page:

Template messages are the only message type that can be sent outside of a customer service window, to reach out to users.

A template is not written at send time. It is registered in advance and approved by Meta, in one of three categories: marketing, utility or authentication. The policy is blunt about who may start a conversation: “You may only initiate conversations using an approved Message Template”.

So once the window shuts, a reply is not a reply any more. You are re-opening the conversation, and the platform treats that as reaching out. Meta’s worked example on the pricing page shows the moment: at hour 26 the window closes, because “24 hours have passed since the user last messaged you”, and the same row records that “you can no longer send non-template messages”.

Service message or template message, and why the difference is not cosmetic

Read carelessly, “service message” looks like a billing word and “template” looks like a formatting word. They are neither. The category decides whether you are permitted to send at all. Meta’s pricing update page puts it plainly:

Thus non-template messages can only be used to respond - not reach out - to users

Two consequences follow, each worth stating on its own:

• A template sent inside the window is still a template message. It does not become a service message by arriving during an open window. In Meta’s example a utility template at hour 4 costs nothing because the window is open, and the same template at hour 30 is charged because it is not.
• Content does not decide the category. Whether a message is a template is a question of how it was registered and sent, not how it reads.

Meta’s own example of a window-opening inbound is a customer asking “Do you have this in a Small?”. Everything you can say back to that in your own words, you can say for 24 hours and not after.

A second clock runs alongside it, and it is not the same clock

If someone reaches you through a Click to WhatsApp ad or a Facebook Page button, a free entry point window opens too. Meta is careful about what that does and does not buy you:

FEP windows remain open for 72 hours. While open, you can send any type of message to the user at no charge. Note, however, that the customer service window is independent of the FEP window, so if the customer service window closes, you will only be able to send template messages.

Free is not the same as allowed. Only the 24-hour window grants permission to write freely.

What changes on 1 October 2026

Nothing about the window. Meta says so directly on the pricing page:

There is no change to when a service message can be sent - it still can only be sent in an open 24-hour customer service window which opens and resets with each user message.

What changes is the price of using it, and what a service message costs from 1 October is that change in full, allowance and delivery stop included. Service messages have been free since November 2024. As of 1 October 2026 Meta will charge for them per message, “consistent with how Meta charges for template messages. These messages have not been charged since November 1, 2024.” The rate is not a new rate card of its own: “By market, rates for service messages will be the same as the rates for utility and authentication messages.” Which market you are in is therefore the question that decides the amount, and what Meta’s rate card publishes and what it leaves in a file is the harder half of answering it. There is no volume discount, and Meta states that explicitly: “Meta will not offer volume tiers for service messages.”

Two further changes matter to anyone replying rather than sending. Utility templates used as a reply inside an open window also become billable on the same date, having been free since July 2025. And Meta records a monthly free allowance: “Each business phone number has one shared free tier of 1,000 delivered service messages per month”, of which “Unused service messages in the free tier do not roll over”. That is Meta’s allowance on Meta’s platform, quoted here as a platform mechanic. It is not an offer of ours.

One consequence is a hard stop rather than a bill: without a payment method on the WhatsApp Business account, “Meta will stop delivering service messages as of when they become charged on October 1, 2026.”

What the rule actually permits

A tool that works only inside this window can do exactly one thing: answer a message a customer already sent, within 24 hours of them sending it. It cannot start a conversation, follow up on day three, or reach anyone who has not written first. Those are template operations, governed by rules this page does not cover.

Google has a comparable published rule for review replies, where a rejected reply’s reason appears in an API and not in the dashboard: it is documented here.

One note for anyone checking this themselves. The older URL for this rule, developers.facebook.com/docs/whatsapp/cloud-api/guides/send-messages, returned a Page Not Found when we fetched it on 19 September 2026. The rule now sits on the Service messages page under /documentation/business-messaging/whatsapp/, cited above. A page that has moved may have been reworded while it moved, which is why every quotation here carries the date we read it.