snipe-it/app/Exceptions/CheckoutNotAllowed.php

<?php

namespace App\Exceptions;

use Exception;
class CheckoutNotAllowed extends Exception
{

    private $errorMessage;

    function __construct($errorMessage = null)
    {
        $this->errorMessage = $errorMessage;

        parent::__construct($errorMessage);
    }
    public function __toString()
    {
       return is_null($this->errorMessage) ? "A checkout is not allowed under these circumstances" : $this->errorMessage;
    }
}