Currently unable to handle this request. HTTP ERROR 500 when i deployed my laravel 5.5 application

I tried deploying my laravel application to my sub domain test.domain.com. I uploaded my files inside Public_html/test folder then i moved all the files inside public folder to the root folder test folder. After that i changed the credentials in my index.php:

before:

require __DIR__.'/../vendor/autoload.php';
$app = require_once __DIR__.'/../bootstrap/app.php';

now:

require __DIR__.'/vendor/autoload.php';
$app = require_once __DIR__.'/bootstrap/app.php';

When i tried visiting the website i get this error:

test.domain.com is currently unable to handle this request. HTTP ERROR
500

I found this error in the error_log file:

 PHP Parse error: syntax error, unexpected '?' in vendor/laravel/framework/src/Illuminate/Foundation/helpers.php on line 233

My site has SSL and The Php version is 7.2

Any help would be appreciated. Thanks.

via Chebli Mohamed