error message

after I activated in plugin page.

but, appear error message.

I hope that as soon as the error is resolved.

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘os_popup_load_scripts’ not found or invalid function name in /home/myurl/public_html/wp-includes/plugin.php on line 525

https://wordpress.org/plugins/popup-for-interactive-content-by-opinionstage/