how to customize request validation array laravel code example

Example 1: how to add an custom error to validater error in laravel

if (request('event') == null) {
    $validator->errors()->add('event', 'Please select an event');
}

Example 2: laravel validation

/**
 * Store a new blog post.
 *
 * @param  Request  $request
 * @return Response
 */
public function store(Request $request)
{
    $validatedData = $request->validate([
        'title' => 'required|unique:posts|max:255',
        'body' => 'required',
    ]);

    // The blog post is valid...
}