Problem with model

I tried to make a fire with a model like this

PHP Code:

function getByUsername($username)
{
return $this
->select('id')
->where('username',$username)
->asObject()
->first(); 


Running normal on localhost (linuxmint, php7.2), but in vps (centos, php7.1) error and display message 
"whoops! we seem to have hit a snag. Please try again later"
can someone explain this?

set your environment to development and you won't get the Whoops page. You'll get an error message.

Simpler is always better

set your environment to development and you won't get the Whoops page. You'll get an error message.

Thanks. 
Solved. 
This App need php-mbstring.