ldc-supportweb/app/Http/Requests/CreateMessage.php

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class CreateMessage extends FormRequest
{
    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'message' => 'required|min:20',
            'file_message' => 'sometimes|mimes:jpeg,jpg,png,pdf|max:2048'
        ];
    }
}