edit: nevermind

hello i think not necessary your router pass parameter this system

Route::group(['prefix' => '/admin'], function(
Route::get('/blog/post/{post_id}/{$end}', [
    'uses'  => 'PostController@getSinglePost',
    'as'    => 'admin.blog.post'
]);

});

because you pass two parameter post_id and end so (&) not necessary . and easily pass two parameter this function

public function getSinglePost($post_id, $end = 'frontend') {


 } 

your write code Route::get('/blog/post/{post_id}&{$end}',

{post_id} one parameter and {end} second parameter laravel route pass parameter {$end} not allow so right code /{post_id}/{end}

thank you