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.

When it closes, you cannot continue with free-form messages. Use an eligible approved template if you have permission to contact the person. Approval permits a template attempt; it does not guarantee delivery.

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 an operating deadline. Once the window has closed, you cannot answer with free-form content. Use an eligible approved template to re-engage the customer, then continue with free-form content if they reply.

To initiate an exchange outside an open window, send an approved template. Your first response to an incoming customer message can use free-form content while the window is open, with a number of your own. Bird's shared numbers carry managed templates only.

Bird tracks the window for you. A free-form send into a closed one is refused when you make the request: POST /v1/whatsapp/messages returns a 422 WhatsAppServiceWindowClosed (E15044), and nothing is created or charged. Use an eligible approved template to re-engage the contact, subject to their permission and the current account, template, and delivery restrictions. Their reply opens a new window for free-form content. If the window closes in the moment between the request and dispatch, the message is created and then fails, with service_window_expired on it. 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.