You should remove '.' in DbConnect.php and DbHandler.php

DbConnect.php

include_once dirname(__FILE__) . './Config.php';

-> include_once dirname(__FILE__) . '/Config.php';

DbHandler.php

include_once dirname(__FILE__) . './Config.php';

-> include_once dirname(__FILE__) . '/Config.php';

That make 2 file include exact what they need. I change this and the API run very good.

Note: You should add header when you call api by Chrome add-on. Content-Type: application/x-www-form-urlencoded