> ## Documentation Index
> Fetch the complete documentation index at: https://developer.omni.z-api.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> Basic concepts about sending messages in the Omni Z-API API

export const projectName = 'Omni Z-API';

## Overview

The message endpoints in this section allow you to send messages **only when the WhatsApp conversation window is open** (within the 24-hour period). This is a rule from the official WhatsApp Business API.

<Warning>
  The 24-hour conversation window opens when the **customer sends a message to you**. Outside this window, you can only send messages using **Meta-approved templates**. The messages in this section **do not work** outside the conversation window.
</Warning>

### Inside the window (24h)

Did the customer send you a message? Great, the window is open. You can use any endpoint in this section to reply with text, image, audio, video, document, etc.

### Outside the window (after 24h)

If the customer has **not** sent a message in the last 24 hours, the only way to start a conversation is by sending a **message template** previously approved by Meta. Templates are pre-defined messages that you create and submit for approval in the Meta dashboard.

<Info>
  In Z-API (unofficial connection) this limitation didn't exist — you could send messages at any time. In the official API, this rule is mandatory and cannot be bypassed.
</Info>

***

To send a message, you need the recipient's **phone number**, including the country code.

| Format                            | Example         |
| --------------------------------- | --------------- |
| Country code + area code + number | `5511999999999` |

## API Response

When you send a message, the API returns the same response structure you already know from Z-API. This means **no changes are needed** in your code that processes the returns — the fields, types, and formats are identical.

Example response when sending a message:

```json theme={null}
{
  "zaapId": "3999984263738042930CD6ECDE9VDWSA",
  "messageId": "D241XXXX732339502B68"
}
```

<Note>
  We maintain full compatibility with the Z-API response structure. If your application already handles these fields, it will continue working without changes.
</Note>

### Store the messageId

It's very important that you **store the `messageId`** returned, as it's needed for future operations like replying, marking as read, or deleting messages.

<Warning>
  Without the `messageId`, you won't be able to reference the message later to reply, react, or delete.
</Warning>

## Text formatting

You can format message text using WhatsApp special characters:

| Formatting        | Syntax         | Result   |
| ----------------- | -------------- | -------- |
| **Bold**          | `*text*`       | **text** |
| *Italic*          | `_text_`       | *text*   |
| ~~Strikethrough~~ | `~text~`       | ~~text~~ |
| `Monospace`       | ` ```text``` ` | `text`   |