php - Problems with Laravel Controller class

Solution:

Everything seems to be fine with your code. Confirm with a directory of the controller must be

app\Http\Controllers\Admin

Or make changings

$this->routes(function () {
        Route::middleware('web')
            ->namespace('App\Http\Controllers')
            ->group(base_path('routes/web.php'));

without using getting namespace value here as a variable in RouteServiceProvider.php.

Solution:

If you are using Laravel 8, it's best to use the new route syntax like so:

use App\Http\Controllers\Admin\PlanController;

Route::get('/admin/plans', [PlanController::class, 'index'])->name('plans.index');

Make sure the controller is in the correct directory app/Http/Controllers/Admin

Solution:

You can describe the full namespace in your route;

Route::get('admin/plans','App\Http\Controllers\Admin\PlanController@index')->name('plans.index');