Before we start it is indicated to have the debug enabled. To be sure that debug mode is enabled wordpress, go to the wp-config file and add next lines
//enable debug
define('WP_DEBUG', true);
//log debug info
//log file will be located in the wp-content directory.
//Make sure that the debug file have write permissions on the server
define('WP_DEBUG_LOG', true);
//do not display debug info on page
define('WP_DEBUG_DISPLAY', false);
For more information about enabling debug on wordpress, check out the developer docs at wordpress