If enabled, any error on the server side will be sent in the response. Set the debug option to
$config['debug'] = true;
If you get an unexpected error (Oops! Something went wrong.), you can use browser dev tools to see the errors and response from the server.
In Google Chrome, right-click and select Inspect, or use the keyboard shortcut: Ctrl+Shift+I (or Cmd+Opt+I on Mac).