{"id":3166,"date":"2026-11-11T11:19:21","date_gmt":"2026-11-11T05:49:21","guid":{"rendered":"https:\/\/www.smsgatewaycenter.com\/blog\/?p=3166"},"modified":"2026-11-11T11:19:24","modified_gmt":"2026-11-11T05:49:24","slug":"whatsapp-24-hour-customer-service-window-state-machine","status":"publish","type":"post","link":"https:\/\/www.smsgatewaycenter.com\/blog\/whatsapp-24-hour-customer-service-window-state-machine\/","title":{"rendered":"The WhatsApp 24-Hour Window as a State Machine: Session Replies, Templates and a Send Router That Never Guesses"},"content":{"rendered":"\n

The WhatsApp customer service window decides whether you can send a free-form reply or need an approved template, and it follows the customer’s last message, not yours. This guide shows how to track the window from the MO webhook and the inbox API, normalise their different timestamp units, derive the window instead of counting it, leave a safety margin at the edge, and route every send to a session reply, a template or a hold.<\/p>\n\n\n\n

\"A<\/a>
Every customer message restarts the clock. Every send asks the clock first.<\/figcaption><\/figure>\n\n\n\n

Table of Contents<\/h1>\n\n\n\n
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  1. The Short Answer<\/a><\/li>\n\n\n\n
  2. TL;DR<\/a><\/li>\n\n\n\n
  3. What Opens, Resets and Closes the Window<\/a><\/li>\n\n\n\n
  4. Two Clocks: the Service Window and the Free Entry Point Window<\/a><\/li>\n\n\n\n
  5. Where the Window Shows Up on the Platform<\/a><\/li>\n\n\n\n
  6. The Timestamp Trap: Seconds on the Webhook, Milliseconds in the Inbox<\/a><\/li>\n\n\n\n
  7. The Window Key Is a Pair of Numbers<\/a><\/li>\n\n\n\n
  8. The State Machine<\/a><\/li>\n\n\n\n
  9. The Data Model: Store Messages, Derive the Window<\/a><\/li>\n\n\n\n
  10. Recording Inbound Messages in Python<\/a><\/li>\n\n\n\n
  11. Asking the Inbox When You Have No State<\/a><\/li>\n\n\n\n
  12. The Send Router: Session Reply, Template or Hold<\/a><\/li>\n\n\n\n
  13. Leave a Margin at the Edge<\/a><\/li>\n\n\n\n
  14. Sending a Session Reply on WAApi\/send<\/a><\/li>\n\n\n\n
  15. When a Session Send Fails<\/a><\/li>\n\n\n\n
  16. Agent Queues and Replies That Wait Overnight<\/a><\/li>\n\n\n\n
  17. What the Window Does to Your Bill<\/a><\/li>\n\n\n\n
  18. Decision Matrix<\/a><\/li>\n\n\n\n
  19. Launch Checklist<\/a><\/li>\n\n\n\n
  20. Unspecified Behaviour and How to Code Around It<\/a><\/li>\n\n\n\n
  21. FAQs<\/a><\/li>\n<\/ol>\n\n\n\n

    The Short Answer<\/h2>\n\n\n\n

    When a customer messages your WhatsApp number, a 24-hour customer service window opens. While it’s open you can send ordinary free-form messages, which this platform calls session messages: you send them through WAApi\/send<\/code> with no templateName<\/code>. When it closes, only approved templates go through. Every new message from the customer resets the timer to a fresh 24 hours. Your own replies don’t.<\/p>\n\n\n\n

    Don’t confuse this with the old 24-hour conversation pricing. Meta replaced that with per-message pricing on 1 July 2025, but the window itself didn’t go anywhere. It still decides whether a free-form message is allowed at all, and under per-message pricing it also decides whether a utility template is free or charged.<\/p>\n\n\n\n

    So the window isn’t something you open and close. It’s a fact you derive: “the newest message this customer sent to this business number, plus 24 hours.” Build it that way. Store every inbound message once, keyed on its WhatsApp message id, from both the MO webhook and the inbox API. Convert the webhook’s timestamp<\/code> (a string of seconds) and the inbox’s timestamp<\/code> (a number of milliseconds) to one unit before they touch each other. Compute the window as MAX(at_ms) + 24 h<\/code> per business and customer pair. Then put one router in front of every send that picks a session reply when the window is open with a safety margin, an approved template when it isn’t, and a hold when there’s no template to use.<\/p>\n\n\n\n

    TL;DR<\/h2>\n\n\n\n