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PHP Fatal error: Class "X" not found
====================================

### [\#PHP](https://rocketeersapp.com/knowledge/php)

This fatal error means PHP could not load a class you referenced. Almost always a namespace mismatch, a wrong file name, or an autoloader that needs regenerating.

 Published by [Mark van Eijk](https://rocketeersapp.com/author/mark-van-eijk) on June 23, 2026 · 1 minute read

1. [About the error](#content-about-the-error)
2. [Why do I see this error](#content-why-do-i-see-this-error)
3. [Solution](#content-solution)
4. [Check the namespace matches the path](#content-check-the-namespace-matches-the-path)
5. [Import the class](#content-import-the-class)
6. [Regenerate the autoloader](#content-regenerate-the-autoloader)

[\#](#content-about-the-error "Permalink")About the error
---------------------------------------------------------

 ```
PHP Fatal error: Uncaught Error: Class "App\Services\Invoice" not found

```

PHP tried to use a class and couldn't find a definition for it. With Composer's PSR-4 autoloading, the class name and namespace must map exactly to a file on disk, and any mismatch breaks that lookup.

[\#](#content-why-do-i-see-this-error "Permalink")Why do I see this error
-------------------------------------------------------------------------

- The **namespace** declared in the file doesn't match its folder.
- The **file name** doesn't match the class name (PSR-4 is case-sensitive, and so is Linux).
- You forgot a `use` statement, so PHP looks for the class in the current namespace.
- The class is new and the autoloader hasn't been regenerated.
- A typo in the class name.

[\#](#content-solution "Permalink")Solution
-------------------------------------------

### [\#](#content-check-the-namespace-matches-the-path "Permalink")Check the namespace matches the path

Under PSR-4, `App\Services\Invoice` must live at `app/Services/Invoice.php` and declare:

 ```
namespace App\Services;

class Invoice
{
    // ...
}

```

The file name (`Invoice.php`) must match the class name exactly, including case. This works on macOS (case-insensitive filesystem) and then breaks on a Linux server, a very common "works locally, 500 in production" trap.

### [\#](#content-import-the-class "Permalink")Import the class

If the class is in another namespace, add a `use` statement at the top of the file:

 ```
use App\Services\Invoice;

$invoice = new Invoice();

```

### [\#](#content-regenerate-the-autoloader "Permalink")Regenerate the autoloader

If the class genuinely exists and is named correctly, Composer's autoload map may be stale:

 ```
composer dump-autoload

```

For framework classes resolved through the container (controllers, etc.), the symptom is slightly different, see [Target class does not exist in Laravel](/target-class-does-not-exist-laravel).

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