Using an external App with laravel

I developed a website using laravel 5.2, but the problem an facing now is link it to an existing App like existing billing system, and livechat app. Is it possible to just upload the folder to my laravel and call it directly?

Example: http://ift.tt/2aMDlFY

where '/billing' is the directory of the already existing billing system.

If its possible how do I go about it?

Am using laravel 5.2

via Chebli Mohamed