Fix Laravel 'Target class [Controller] does not exist'

Since Laravel 8 removed the default controller namespace prefix, string-based route definitions are the number one cause of this error. Here is the modern, reliable way to declare routes.

Fix: Use the Class-Based Route Syntax

// ❌ Old string syntax (relies on a namespace prefix that no longer exists)
Route::get('/users', 'UserController@index');

// ✅ Import the class and reference it
use App\Http\Controllers\UserController;

Route::get('/users', [UserController::class, 'index']);

Check the Namespace Matches the Path

A controller in app/Http/Controllers/Admin/ must declare namespace App\Http\Controllers\Admin;. A mismatch here produces the same error.

Rebuild the Autoloader

composer dump-autoload
php artisan optimize:clear