The most important rule on the WhatsApp API
If you remember nothing else about WhatsApp Business Platform pricing and rules, remember this: every time a customer messages you, a 24-hour window opens. Within that window, you can send any reply you like, including text, images, files, voice notes and interactive messages, with no template required. Once it closes, you can only re-engage them using a pre-approved template.
How the window starts and resets
The clock starts the moment a user sends you a message. Every new inbound message resets the clock to a fresh 24 hours. Outbound messages from your side do not reset it; only customer replies do. This means if a customer messages you at 9am Monday and you reply at 10am, you have until 9am Tuesday to keep replying without templates.
What you can do inside the window
Anything reasonable. Text replies, document attachments, product catalogs, location pins, voice notes, interactive button menus, list messages and free-form follow-ups are all permitted as long as they relate to the customer's enquiry. The window is designed to enable real conversational support.
What you cannot do inside the window
Promotional content unrelated to the original conversation is still subject to opt-in rules and quality scoring. The window is not a free pass to spam. If a customer asked about a refund and you respond with a marketing offer for a new product, expect complaints and a falling quality rating.
Outside the window
Once 24 hours pass without a customer reply, you must use an approved template message to re-engage. Templates require category classification, formal approval, and they are charged at category-specific rates. Free-form messages sent outside the window simply will not deliver.
Why Meta enforces it
The window protects users from being messaged at random by businesses they have not interacted with for days or weeks. It pushes companies toward conversation-led support and away from drip-marketing patterns better suited to email.
Practical tips
Build internal alerts so agents know when a window is closing on an unresolved chat. Train teams to either resolve issues within the window or set the customer's expectation that the next contact will arrive as a template. Use utility templates for follow-ups and reserve marketing templates for new offers.
Common misunderstandings
The window is per customer, not per agent or per department. Transferring an internal ticket does not reset it. The window is also unrelated to your business hours; it ticks during weekends, holidays and overnight just the same.