Error on home page – function 'wpdm_popup_link' not found or invalid function

This error is on my home page

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘wpdm_popup_link’ not found or invalid function name in /home/pcweb/public_html/wp-includes/plugin.php on line 505

website: http://policecreditgy.com/

https://wordpress.org/plugins/download-manager/