What is the messaging window?
The messaging window is the period during which you can send messages without format restrictions.
24-hour window (default)
Whenever a contact sends you a message, you have 24 hours to reply with free-form messages (no HSM template needed). This count restarts with each message received.
Example:
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Monday, 10:00 → contact sends a message
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Monday, 10:01 to Tuesday, 10:00 → you can send free-form messages
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Tuesday, 10:01 onward → you need to use an HSM template
72-hour window (Click to WhatsApp)
If you use Click to WhatsApp ads (ads that lead to WhatsApp), Meta offers an extended 72-hour window to send free-form messages. This only works with the WhatsApp Cloud API.
Requirements to enable 72h:
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Connect the account via the WhatsApp Cloud API (not via WhatsApp Business/Evolution)
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Have ad campaigns set up in Meta Ads Manager
What is an HSM (Highly Structured Message)?
An HSM template is a message pre-approved by Meta that you can use outside the 24h/72h window to reach cold leads or re-engage contacts who didn't reply.
HSM template characteristics
| Aspect | Detail |
|---|---|
| Approval | Submitted for Meta approval; takes minutes to hours |
| Components | Header (text, image, video, document), body, footer, buttons |
| Variables | Use var_ for personalization (e.g., var_business_name = company name) |
| Legal requirement | Must clearly indicate opt-in or prior context of consent |
| Limit per number | Maximum of 6,000 templates per WhatsApp number |
| Reuse | An approved template can be reused without limit |
When do you need an HSM?
| Situation | Required? | Why? |
|---|---|---|
| Replying to a message received within 24h (or 72h) | No | You're inside the window |
| Sending a first-contact campaign (cold outbound) | Yes | You're outside the window |
| Following up with contacts who didn't reply within the window | Yes | The window has expired |
| Smart Follow-up after a closed conversation | Yes | Re-engagement requires a template |
| AI agent starting a conversation | Yes | Always outside the window |
Smart Follow-up and the window rules
Nuvia's Smart Follow-up feature automatically respects WhatsApp's rules:
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Inside the 24-hour (or 72-hour) window: sends a free-form message, no template
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Outside the window: automatically switches to an HSM template
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No template available: the Follow-up isn't sent; you see a warning
Set up the templates you'll use in Follow-ups in advance. Don't leave approval to the last minute.
Daily sending limits (Tiers)
WhatsApp limits how many messages you can send per day, depending on your account:
| Tier | Daily limit | Typical use case |
|---|---|---|
| Tier 1 | 1.000 | New accounts, initial tests |
| Tier 2 | 10.000 | Small SDR teams |
| Tier 3 | 100.000 | Mid-sized operations |
| Tier 4 | No limit | Companies at scale (100K+ contacts/day) |
You start at Tier 1. To scale up, show consistent quality (low block rate) for 7 days.
WhatsApp rules that affect your campaigns
Don't send cold promotional messages without a template
If you don't have an open window (the contact hasn't replied in more than 24h/72h), any message must go through an HSM. Sending it any other way violates WhatsApp's policies, and your account may be restricted.
HSM templates must be clear and respectful
Meta rejects templates that:
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Look like spam (e.g., “Grab it NOW! UNMISSABLE DISCOUNT!!!”)
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Ask for sensitive data (e.g., passwords, credit card)
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Include suspicious links or unknown URL shorteners
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Suggest implied consent (“you will be added to…”)
Avoid account blocks
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Don't use the same message for hundreds of contacts without variation
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Don't send test messages to real numbers (use WhatsApp test numbers)
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Respect your Tier limit; don't exceed your daily quota
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Monitor the block rate; above 5%, investigate your templates