WhatsApp API Error PATTERN_MISMATCH in WhatsApp Flows

If you're building a flow on WhatsApp and hit a PATTERN_MISMATCH error, you're not alone. This is one of those errors that can be confusing at first, but it usually comes down to formatting issues in your JSON.

Here’s what the error typically looks like:

PATTERN_MISMATCH

Property (propertyName) should only consist of alphabets and underscores.

Property (propertyName) should be of type '(type)' or have dynamic data format...

Let’s unpack what this means and how you can fix it quickly.

The Problem

Here’s a broken example that causes a PATTERN_MISMATCH:

{
  "screens": [
    {
      "id": "FIRST_1",
      "layout": {
        "children": [
          {
            "type": "TextInput",
            "name": "Description",
            "label": "Enter decsription",
            "max-chars": "Hundred"
          }
        ]
      }
    }
  ]
}

There are two main issues here:

 1. id Format Issue

id: "FIRST_1": WhatsApp Flow screen IDs must contain only alphabets and underscores.
Change it to "FIRST" or "FIRST_SCREEN".

2. max-chars Must Be a Number or Dynamic Expression

"max-chars": "Hundred": This should be a number like 100 or a dynamic variable like "${data.limit}".

The Fix

Here’s the corrected version:

{
  "screens": [
    {
      "id": "FIRST_SCREEN",
      "layout": {
        "children": [
          {
            "type": "TextInput",
            "name": "Description",
            "label": "Enter description",
            "max-chars": 100
          }
        ]
      }
    }
  ]
}

Now everything is in the proper format:

• The screen ID uses only alphabets and underscores.

• max-chars is a valid number.

Common Format Rules in WhatsApp Flows

Here’s a quick reference to avoid PATTERN_MISMATCH errors in the future: