The 24-hour window

WhatsApp protects customers from unwanted messages with one rule, enforced by Meta and by MeAPI:

You can send free-form messages only within 24 hours of the customer’s last message to you. Outside that window, only approved templates.

	Window open (customer wrote < 24 h ago)	Window closed
Text, media, interactive	✅ Allowed	❌ 409 WINDOW_CLOSED
Template	✅ Allowed	✅ Allowed
Meta charge	Service messages: first 1,000 per business number per month free, then charged. Utility templates charged	Per delivered template (marketing / utility / authentication)

• The window opens (or restarts) every time the customer messages you — text, a button tap, a reaction, anything.
• Your own messages do not extend it.
• MeAPI checks the window for you: a free-form message outside it is refused with 409 WINDOW_CLOSED instead of failing later at Meta.
• The panel’s inbox shows a live countdown for each chat.

Patterns that work

• Start with a template, e.g. an order update with a “Track order” or “Talk to us” button. When the customer replies or taps a quick-reply button, the window opens and you can continue freely.
• Reply fast. The first 1,000 service replies per number each month are free; after that Meta charges them at its service rate.
• Follow up with templates. After 24 hours, use a utility template (“Your appointment is tomorrow…”) or a marketing template for offers.
• Respect opt-outs. Contacts who send STOP are refused (403 OPTED_OUT) until they send START.