The WhatsApp customer service window

WhatsApp does not let a business message whoever it likes whenever it likes. What you are allowed to send depends on whether a conversation is open, and Meta calls that open period the customer service window.

The window opens when a WhatsApp user messages you or calls you, and it runs for 24 hours. Every new message or call from that same user resets it to a fresh 24 hours, so an active back-and-forth keeps the window open indefinitely.

While it is open, you can send free-form content: text, images, documents, and the other message types Meta allows in a live conversation. Nothing needs prior approval, because the customer started the exchange. Meta calls these service messages, and charges nothing for them: non-template messages inside an open window are free, as are utility templates delivered inside one (WhatsApp pricing).

When it closes, free-form content stops reaching that person. An approved template is the only thing that does.

Nothing you send opens a window on its own terms. A template you send to someone who has not written to you starts a business-initiated conversation, and it still needs the opt-in Meta requires before you message anyone.

Meta also documents a known issue: in rare cases a message arrives from a user and you cannot reply inside the window it should have opened.

It puts the customer in control of who talks to them. A business can always answer a question it was asked, and cannot use that answer as a door into unsolicited messaging a week later. The template requirement outside the window is what makes the difference enforceable: every business-initiated message has passed Meta's review before it is sent.

For your side of the exchange, this is also a service-level expectation. A question that sits unanswered for more than a day cannot be answered in the same conversation at all.

Whatever you send first is a template, which is the shape the window requires anyway: it has already been approved. Free-form content inside an open window needs a number of your own, because Bird's shared numbers carry managed templates only.

Bird does not track the window for you. A free-form send outside one is accepted and then fails, with service_window_expired on the message. Sending WhatsApp messages covers both content kinds, and WhatsApp templates the templates available to you.

Time in the window is worth watching for anything conversational. If a customer's question comes in and the reply depends on a human, the clock started when their message arrived, not when someone picked it up.