What is the session response in the WhatsApp API

The session reply in the WhatsApp API is the mechanism that allows a business to respond to a user's message within a 24-hour window from the customer's last message. In plain terms: when a customer writes to you on WhatsApp, you have one day to reply using a session reply, with no additional template cost and no need for prior approval. It is the most direct and natural way to attend to someone who reaches out to you.

Why does it matter to an SME?

If you have a business and you provide support via WhatsApp, the session reply is the heart of customer service. Because when a customer writes to you, they expect a quick response, and the WhatsApp API gives you a 24-hour window to respond without having to use templates (those pre-approved messages that are only for starting conversations). For an SME, that means you can answer questions, resolve complaints, or confirm orders spontaneously, without bureaucratic hurdles.

How is it used in practice?

In practice, when a customer writes to you on WhatsApp, Meta's API opens a 'session window' that lasts 24 hours. During that time, you can freely send any message: text, images, audio, etc. To reply, your system (or your management tool) simply sends the message using the API's messages endpoint, and Meta delivers it as a session reply. If the window closes, you can no longer reply that way: you have to use an approved template, which usually has a cost and requires prior approval.

Concrete and complete example

Imagine you have an online clothing store. A customer writes to you on WhatsApp: 'Do you have the black t-shirt in size M?' That message opens the session. During the next 24 hours, you can reply: 'Hello! Yes, we have it. Should I reserve it for you?' You can also send them a photo of the product, a payment link, or an audio. All of that is a session reply. If the customer does not respond and after 25 hours you want to write 'Are you still interested?', you can no longer do so: the session has closed. You would have to use an approved template (like a follow-up one) and pay for it.

What it is confused with and how it differs

The session reply is often confused with the template message (HSM). They are different things: the session reply is a free reply within the 24-hour window, at no cost and without approval; the template is a pre-approved message used to start a conversation or resume it after the session has expired, and it usually has a cost. It is also confused with the 'auto-reply' or 'welcome message': that is an automatic session reply, but the session remains the underlying concept.

Common mistakes made by SMEs

• Believing that the 24-hour window renews with each of your replies: no, it only renews when the customer replies. If you reply and the customer does not respond, the session still closes 24 hours after their last message.
• Using templates to reply within the session: that is a mistake, because templates have a cost and are colder. Whenever you can, reply with a free message.
• Not having a system that alerts you when the session is about to expire: you lose customers and miss the chance to reply at no cost.
• Thinking that the session reply is unlimited: there are limits on messages per second and per day, which vary depending on the quality level of your number. If you do not respect them, you can get banned.

What happens if you do not take the session into account?

If you do not take the session window into account, you can make two serious mistakes: first, trying to reply outside the window without using a template, which the API rejects and can cause temporary blocks. Second, not replying in time and losing customers: 70% of customers expect a reply in less than 5 minutes, and if they do not receive it, they go elsewhere. Additionally, if you use templates unnecessarily, you waste money.

How does it relate to the official Meta API?

The session reply is a concept defined by Meta's official WhatsApp API (WhatsApp Cloud API). Meta sets the rules: the 24-hour window, the allowed message types, the speed limits, and the costs. Any tool that uses the official API (like Wando) is subject to these rules. That is why it is key to choose a tool that manages sessions well and alerts you when one is about to expire. Wando, for example, uses Meta's official API and its AI suggests replies that you approve with one click, always within the session window.

When the session reply does NOT apply

The session response does not apply when the customer never wrote to you first (there is no open session). In that case, you can only start a conversation with an approved template, and the cost is higher. It also does not apply if the customer blocked you or if the number is not valid. Additionally, there are special cases: if the customer writes to you and then deletes the message, the session still opens, but if they delete the number, it does not. In short: without an incoming message, there is no session.

Concrete setup: which screens to touch

To use the session response, you don't need to configure anything special in the API: it is the default behavior when you respond to an incoming message within 24 hours. But you need to configure the environment so that this happens without friction.

In the WhatsApp Cloud API, you configure a webhook that receives incoming messages. That webhook must respond quickly (less than 10 seconds) so Meta doesn't retry the delivery and duplicate events. Then, the message sending endpoint (/messages) accepts text, image, audio, etc. No extra steps.

What you do need to touch is window management: your tool (or your code) must store the timestamp of each customer's last incoming message and compare it to the current time. If the difference is less than 24 hours, you respond with a free-form message; otherwise, only templates.

• Webhook: configure the URL and verify the token in the Meta panel.
• Sending endpoint: use the same for sessions and templates; the API decides based on context.
• Timestamp: store the time of the incoming message (Meta's 'timestamp' field, not your database's).

How to verify it worked and what to check if it fails

The simplest test: send yourself a message from a customer number to your business number and reply from your tool. If the message arrives as a session reply, you'll see it in the conversation history with a 'session' indicator (in most tools) or in the API logs.

If it doesn't work, the first thing to check is the webhook: did the event arrive? Did you respond with 200 OK? Then, the timestamp: are you using the correct field? If you use the row creation one in your database, you'll see the session closes before or after it should.

Also check your number's quality rating. If it's 'low', Meta may limit delivery of session messages. That's visible in Meta's panel, in the phone numbers section.

• Webhook: incoming events and 200 response.
• Timestamp: which one you're saving and where it comes from.
• Number quality: if it's low, messages may not be delivered.

What changes based on business size

In a one-person business, the session window is managed in your head: you know who wrote to you and when. The risk is forgetting and the session closing. A tool that warns 'you have 2 hours left' saves you.

In a fifteen-person business, the problem is different: several agents handle the same WhatsApp and nobody knows if the session is still open. There you need multi-agent with shared history and expiry alerts per conversation. Speed limits also matter: with fifteen agents replying, you can hit the messages-per-second limit if you don't coordinate.

The window rule is the same, but the operation is different. A small business can survive without automating expiry alerts; a large one cannot.

• 1 person: manual alerts, risk of forgetting.
• 5-15 people: multi-agent, shared history, automatic alerts.
• Speed limits: more agents = more coordination.

What the official documentation says and what is left to each platform's discretion

Meta's official documentation defines: the 24-hour window opens with the user's last incoming message, renews with each customer response, and within the window free-form messages can be sent. That is what is written.

What Meta does not define is how your tool notifies you that the window is about to expire, nor how it displays history, nor how it prioritizes conversations. That is up to each platform. It also does not define how to handle a customer who writes at 2 AM: the window still runs, but you reply in the morning. There, the platform can offer scheduled auto-replies so as not to leave the customer unanswered.

In short: session rules are Meta's, but the management experience is the tool's. Choose one that helps you not miss windows.

• Meta: duration, renewal, message types.
• Platform: alerts, history, auto-replies.
• You: decide how to handle within the window.

Second-order questions that remain after understanding the concept

You already know what the session window is. Now you ask: what happens if the customer writes at 23:50 and the session expires at 23:50 the next day? Do you reply at 9 AM and the customer is no longer there? The answer is that the window renews only if the customer responds, not if you respond.

Another one: can you send a template within the session? Yes, but it's pointless: the template has a cost and is colder. Only use it if you want to start a new conversation or resume an expired one.

And the most practical one: how do I keep the session from slipping away? With a tool that shows you the remaining time per conversation and alerts you before it expires. Otherwise, you're left scheduling a manual reminder.

• Does the session renew with my response? No, only with the customer's.
• Can I send a template within the session? Yes, but it's not advisable.
• How do I avoid it slipping away? Alerts and prioritization.