If you get any error or want to debug anything, then enable the error log.
Note: Once you've completed the debugging, please remember to revert the settings back. Otherwise it'll create unnecessary logs in your server and waste spaces.
public $threshold = 0;
If you would like to see the errors, you can enable the development mode. It's not recommended in production.
CI_ENVIRONMENT = development
Note: Once you've completed the debugging, and you don't want the development mode, just delete .env file;