# Specifics of sending messages to numbers of different countries

### Quick Summary: How to Avoid Message Delivery Issues

If you're experiencing issues where messages aren’t delivered or you notice that a customer’s number appears differently in webhook logs than what you see in your CRM or phone contacts — you're likely facing a **number formatting mismatch**.

{% hint style="info" %}
⚠️ **Note:** This issue typically affects specific countries with special number formatting rules — namely **Mexico, Argentina, and Brazil**.
{% endhint %}

WhatsApp requires phone numbers to follow **country-specific formatting rules**, and using the "visually correct" number (what the user gave you, or what's stored in your system) is often **not sufficient**.

To ensure proper delivery and tracking of messages:

✅ **Always use the WhatsApp** [**Chat ID**](https://support.whapi.cloud/help-desk/faq/chat-id.-what-is-it-and-how-to-get-it) (e.g. `1234567890@s.whatsapp.net`) returned in the webhook or retrieved using the [`checkPhones`](https://whapi.readme.io/reference/checkphones) method.

Here are the most common formatting rules to be aware of:

<table><thead><tr><th width="102">Country</th><th width="206">Formatting Rule</th><th width="208">Example Input</th><th>Required Chat ID Format</th></tr></thead><tbody><tr><td><strong>Mexico</strong></td><td>Insert <code>1</code> after country code <code>52</code>, and remove any <code>11</code> prefix</td><td><code>+52 56 3969 1841</code></td><td><code>5215639691841@s.whatsapp.net</code></td></tr><tr><td><strong>Argentina</strong></td><td>Insert <code>9</code> after <code>54</code>, and remove <code>15</code> from the local number</td><td><code>+54 11 5874 9895</code></td><td><code>5491158749895@s.whatsapp.net</code></td></tr><tr><td><strong>Brazil</strong></td><td>For area codes <strong>11–19, 21, 22, 24, 27, 28</strong>, <strong>add</strong> a <code>9</code> after the area code; otherwise, <strong>remove</strong> it</td><td><code>+55 92 98172 3241</code> → <code>+55 92 8172 3241</code></td><td><code>559281723241@s.whatsapp.net</code></td></tr></tbody></table>

If you're sending messages based on the phone number you received from the client (manually or from CRM) **without adjusting formatting**, there's a high chance the message won't be delivered or matched correctly.

Use this table and `checkPhones` to verify and normalize numbers **before sending**.

***

### Where the Problem Happens

This issue usually becomes visible in one of the following situations:

* You know the customer’s phone number (e.g. collected manually or stored in a CRM), but your message is never delivered.
* You receive incoming messages in the webhook, but the sender's number looks slightly different — for example, it may be missing a digit (such as a leading `9`), or include one that doesn’t match your records.

In all of these cases, the underlying cause is the same: you're using a number in the wrong format — one that **looks correct** to a human, but **isn't recognized** by WhatsApp internally.

> 📍 This problem is most commonly seen in Latin American countries like **Mexico, Argentina, and Brazil**, where mobile numbering rules are more complex and non-standardized.

***

#### Country-Specific Formatting Rules

Some countries require additional adjustments to mobile numbers before they can be used with WhatsApp. These rules are **not obvious** and can lead to delivery failures if not handled properly. Below are the most commonly affected regions:

***

### **Mexico**

**Common issue:** Messages fail to deliver if the number is missing a required `1` after the country code. This applies to all Mexican mobile numbers (including Nextel).

**Rule:**\
Insert a `1` **after the country code `52`** and remove any prefix like `11`. This ensures the number is 13 digits long.

**Incorrect format (as seen in CRM):**\
`+52 56 3969 1841`

**Correct Chat ID format for sending messages:**\
`5215639691841@s.whatsapp.net`

***

### **Argentina**

**Common issue:** If the number includes a `15` prefix or lacks the required `9`, WhatsApp won’t recognize it.

**Rule:**\
Insert a `9` **after the country code `54`** and remove any `15` from the start of the local number. The result should also be a 13-digit number.

**Incorrect format (as given by users):**\
`+54 11 5874 9895` or `+54 15 5874 9895`

**Correct Chat ID format for sending messages:**\
`5491158749895@s.whatsapp.net`

***

### **Brazil**

**Common issue:** WhatsApp may ignore messages if the `9` digit is either wrongly included or omitted. Whether to keep or remove it depends on the area code.

**Rule:**\
For area codes **11–19**, **21**, **22**, **24**, **27**, and **28**, a `9` **must be added** after the area code.\
For all **other area codes**, the `9` **must be removed** if it’s present.

**Incorrect format (based on phone contact):**\
`+55 92 98172 3241` (area code 92 does **not** require the 9)

**Correct Chat ID format for sending messages:**\
`559281723241@s.whatsapp.net`

> 🔎 Tip: If you're unsure how to format a number, use the [`checkPhones`](https://whapi.readme.io/reference/checkphones) method to validate and retrieve the correct WhatsApp ID before sending.

***

### How to Solve the Issue

To avoid delivery issues and mismatched numbers in your system, it's essential to rely on **WhatsApp's actual internal identifier** — the `Chat ID` (e.g. `559281723241@s.whatsapp.net`).

Here’s how to handle it properly in your integration:

#### **1. Use `checkPhones` endpoint to Validate Numbers**

Before sending any message, especially to users in Mexico, Argentina, or Brazil, use the [`checkPhones`](https://whapi.readme.io/reference/checkphones) method to retrieve the correct, WhatsApp-validated Chat ID.

This method checks whether a number is registered on WhatsApp and returns the exact identifier you should use when sending messages.

**Example:**

*Request:*

```bash
curl --request POST \
     --url https://gate.whapi.cloud/contacts \
     --header 'accept: application/json' \
     --header 'authorization: Bearer YOUR_TOKEN' \
     --header 'content-type: application/json' \
     --data '
{
  "blocking": "wait",
  "force_check": false,
  "contacts": [
    "5592981723245",
    "5592981723243"
  ]
}
'
```

*Response:*

```json
{
  "contacts": [
    {
      "input": "5592981723246",
      "status": "valid",
      "wa_id": "559281723246@s.whatsapp.net" // Correct Chat ID
    },
    {
      "input": "5592981723243",
      "status": "invalid" // This number does not have WhatsApp at all
    }
  ]
}
```

The format is <559281723242@s.whatsapp.net> and is [the chat identifier](https://support.whapi.cloud/help-desk/faq/chat-id.-what-is-it-and-how-to-get-it). You should now send all messages **only** to this Chat ID.

#### **2. Use the Chat ID from Incoming Webhooks**

When a customer sends you a message, the webhook includes their Chat ID. That ID is already normalized and confirmed by WhatsApp — it’s the most reliable reference for future communication.