Short answer
For WhatsApp Business Platform, the service window lasts 24 hours from the customer’s last message or call. Free-form replies are possible inside it; outside it an appropriate approved template is required. No business message restarts the window, and the calculation applies at the moment of sending, not drafting. Also honour permissions and opt-outs before sending.
Key verification: The record identifies the last inbound customer message and justifies the message form before sending.
Sources and limitationsAn agent writes a reply the following day and the API rejects it. A conversation visible on screen is not enough to decide whether free-form text is allowed: what counts is when the customer last wrote or called. This guide concerns WhatsApp Business Platform and its API, rather than assuming identical rules for every feature of the small-business mobile application.
The rule: 24 hours from the customer’s last message
The WhatsApp Business Messaging Policy, checked on 27/10/2026, states that you may reply without a template inside the customer service window, which opens and resets with each user message, and that outside it you may only send approved templates. The platform pricing documentation adds that the 24-hour timer starts when the user messages or calls you, that non-template messages can only be sent while the window is open and that templates can be sent at any time.
Two practical consequences follow. No business message resets the window, whether a free-form reply or a template. And the decision is made at the moment of sending, not when drafting.
A fictional timeline with clear margins
| Event | Time | Interpretation |
|---|---|---|
| Customer requests a quote | Monday 09:00 | Inbound reference; expires Tuesday at 09:00 |
| Agent replies | Monday 10:00 | Within the window; does not move the expiry |
| Agent follows up | Tuesday 12:00 | 27 hours have passed: template only |
| Variant: the customer writes | Tuesday 08:30 | New reference; expires Wednesday at 08:30 |
With no new customer message, Monday’s reply does not carry the reference over to Tuesday. If the customer writes again on Tuesday at 08:30, the same 12:00 send can now be a free-form reply. Store the date, time zone and identifier of every inbound message; an interface label such as “yesterday” cannot establish an exact expiry.
What opens the window and what does not
| Event | Does it open or reset the window? | What to do |
|---|---|---|
| Customer message | Yes | Record its time as the new reference |
| Customer call over WhatsApp | Yes | Record the call and its time in the contact history |
| Agent’s free-form reply | No | Do not change the expiry |
| Template sent by the business | No | Wait for the customer to reply |
| Delivery or read receipt of a business message | No | Do not use it as a reference |
If contact starts by voice, the move from chat to call and its continuity are covered in the WhatsApp Business Calling pilot.
Recalculate before sending, not when drafting
A draft prepared on Tuesday at 08:50 is 23 hours and 50 minutes after Monday at 09:00. If the queue sends it at 09:10, 24 hours and 10 minutes have passed: the drafting decision has expired. Reassess the latest inbound message immediately before sending and hold the send if that reference is unavailable.
Edge case: the clock change. A customer writes on Saturday 24 October 2026 at 10:00 mainland Spain summer time, which is 08:00 UTC. In the early hours of Sunday 25 the clocks go back one hour, so the window expires at 08:00 UTC on Sunday, that is, 09:00 winter time, not 10:00. A system that calculates “same time tomorrow” would allow one hour too many. Store times in UTC and convert only for display.
What to check with CallHippo
The CallHippo WhatsApp Business API page describes free-form messages during the 24 hours after a customer makes contact and approved templates outside that period (checked on 27/10/2026). Confirm that the solution is available and how template review works in your account before subscribing. Approval of wording establishes neither recipient consent nor successful delivery.
Templates: category, permission and cost
The pricing documentation classifies templates as marketing, utility and authentication, charges messages when they are delivered and records pricing changes in force since 1 October 2026. Do not copy rates from older guides: check the current table for your country and category. Choose the category by the message’s real purpose; an appointment reminder is not the same as a promotion.
The policy also requires the recipient’s permission to receive messages and that opt-out requests be honoured. In Spain, that permission must comply with the GDPR and other applicable rules; an approved template does not replace it. If several agents share the conversation, keep it visible who replied and when, as suggested in the shared WhatsApp inbox guide.
Exercise without messaging customers
Using an authorised test conversation, prepare cases inside and outside the window and one with a fresh inbound message. Check that the system asks for the correct message form, that the template is still approved and that variables do not change its meaning. Record the error and the final status separately. Avoid bulk retries and do not assume that switching to a template removes recipient blocking. CallsIQ has not performed these sends; what is accepted is a traceable decision, not a delivery promise.
Common mistakes and how to spot them
| Mistake | Symptom | Check |
|---|---|---|
| Counting from the agent’s last message | Rejections of replies that seemed on time | Filter the history to inbound messages |
| Deciding when drafting, not when sending | Rejections of scheduled or queued sends | Recalculate the expiry at the moment of sending |
| Using local time without a time zone | One-hour errors after the clock change | Store and compare times in UTC |
| Retrying a rejection in a loop | Many identical errors within minutes | Read the error code before retrying |
| Using a template to get round an opt-out | Complaints or blocking by the recipient | Check the opt-out list before every send |
From the author's experience
In the WhatsApp-to-contact-centre integrations I have seen, I would require the integration itself to know the user's last message and check the window before sending, while still respecting whatever validation the API applies at send time; the policy allows a free-form reply within the twenty-four hours and requires an approved template outside them. For queued messages that risk expiring before they go out, I would validate the window right at send time and route anything already expired to review, using an approved template only when it applies.
On the template-category mistake, I would check whether a template presented as utility actually contains promotion or upselling, validating category, approval and intended use before activating it; I would not claim a frequency of my own for that mistake without reviewing actual templates. On permission and opt-outs, I would make the recorded permission visible on the contact record, with its source, date and scope, along with any opt-out, and I would apply that same check to automated sending too, so it does not rely solely on an agent remembering to look.
When a client reports that their WhatsApp replies are being rejected, the first thing I would ask for is the exact rejection code, then check the window, message type and template status before verifying recipient, permissions and applicable limits and retrying.
Sources and limitations
Documentary review: . Content type: Documentation-based guide with original exercise.
Linked sources describe the terms and capabilities each provider publishes. Examples that use fictional data are labelled in the text.
Scope: Documentation reviewed on 16 October 2026. Examples are fictional and tests are proposed; CallsIQ has not performed product tests.
- WhatsApp Business Messaging Policywhatsappbusiness.com
- platform pricing documentationdevelopers.facebook.com
- CallHippo WhatsApp Business API pagecallhippo.com
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