> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sayvyai.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Messaging Window

> Understanding WhatsApp 24-hour customer service session rules

# Messaging Window

*This page covers the rules, timers, and state machine lifecycle governing Meta's 24-hour customer service window.*

***

## Session Lifecycle & Window Rules

*Content coming soon.*

* User-Initiated Conversations (UIC) vs. Business-Initiated Conversations (BIC)
* 24-hour sliding window mechanics calculated from the last user message
* Freeform conversational messages vs. pre-approved HSM template constraints

***

## Session State Machine

*Content coming soon.*

* States: `IDLE`, `ACTIVE_24H`, `EXPIRED`, `TEMPLATE_PENDING`
* Transitions triggered by inbound messages, timer expirations, and template replies

***

## Expiration Handling & Fallbacks

*Content coming soon.*

* Graceful degradation when the window closes mid-workflow
* Automatic re-engagement via approved utility templates


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.