I saw that already, username option is missing,
I listened to visitor_guest_setup event and added this
$userInput = ['username' => 'str'];
$output = $this->app()->request()->filter($userInput);
$defaultData['username'] = $output['username'];
I have solved this issue by following follow procedure
Edit file config.php and add below two lines:
$config ['externalDataUrl'] = 'http://mysite.com/forum/data';
$config ['javaScriptUrl'] = 'http://mysite.com/forum/js';
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