Two Errors whilst installing phpBB onto my forums

Question

So auto installer was down on my web host provider and this was the first time trying to install a forums. I do not understand coding so when i cam across these errors i wasn't sure how to fix them. Here are the screenshots:

I downloaded it straight from the phpBB website unedited.

Code:

{
            $json_response = new \phpbb\json_response();
            $json_response->send(array(
                'success'   => true,
            ));
        }