{"error":"Bad Request"} response from custom php - php

Question

I'm completely new to php, and was hoping to get some assistance on understanding this custom script on our server as our full-time dev ended up going on a sudden leave of absence. When visiting our webpage I am getting the error:
{"error":"Bad Request"}
And our dev seems to have created a router.php file that seems to be redirecting all the traffic and thus displaying this error. I'm having a hard time trying to understand where this error is coming from and how I could further troubleshoot it. But here's the code within the router.php
<?php
use util\HttpStatus;
require_once('../vendor/autoload.php');
function module($request)
{
$request = ltrim($request, '/');
$qp = strpos($request, '?');
if ($qp > 0) {
$request = substr($request, 0, $qp);
}
$tokens = explode('/', $request);
return $tokens[0];
}
function __run($request)
{
$modules = [
"dashboard",
"inventory",
"branches",
"promotions",
"feeds",
"websites",
"leads",
"slfleads",
"events",
"media",
"notify",
"callback"
];
$requestedModule = module($request);
if(in_array($requestedModule, $modules)){
file_exists("../services/$requestedModule/_boot.php")
? require ("../services/$requestedModule/_boot.php")
: require ("../$requestedModule/_boot.php");
_boot();
} else {
_blameAndDie();
}
}
function _blameAndDie($reason = null)
{
http_response_code(HttpStatus::BAD_REQUEST);
header("Content-Type: application/json");
echo ($reason === null)
? '{"error":"Bad Request"}'
: '{"error":"Bad Request","reason":"' . $reason . '"}';
die();
}
function _blockAndDie($reason = null)
{
http_response_code(HttpStatus::UNAUTHORIZED);
header("Content-Type: application/json");
echo ($reason === null)
? '{"error":"Forbidden"}'
: '{"error":"Forbidden","reason":"' . $reason . '"}';
die();
}
function _blunderAndDie($reason = null)
{
http_response_code(HttpStatus::INTERNAL_SERVER_ERROR);
header("Content-Type: application/json");
echo ($reason === null)
? '{"error":"Server Error"}'
: '{"error":"Server Error","reason":"' . $reason . '"}';
die();
}
__run($_SERVER['REQUEST_URI']);
?>
Perhaps this is the way it is? but it would be nice to have a splash screen that just says nothing to see here or something because most of the functions are done behind the scene.