using app_path() returns 500 error

Using Laravel 8 with PHP 7.3

This has happened in multiple places where I've had to replace `include_once(app_path() . '\WebClientPrint\WebClientPrint.php');
`  with `app_path('WebClientPrint/WebClientPrint.php')` 

This problem exists in:

`WebClientPrintController.php`
`PrintZPLController.php`
`HomeController.php`
