ProxyPanel/app/Http/Requests/Admin/TicketRequest.php

<?php

namespace App\Http\Requests\Admin;

use Illuminate\Foundation\Http\FormRequest;

class TicketRequest extends FormRequest
{
    public function rules()
    {
        return [
            'uid'      => 'required_without:username|exists:user,id|numeric|nullable',
            'username' => 'required_without:uid|exists:user,username||nullable',
            'title'    => 'required|string',
            'content'  => 'required|string',
        ];
    }
}