Issues with my Easy Sign Up

Just a few days ago, it worked just perfectly but today, after a customer fills in information and clicks ‘Send’, instead of redirecting to the specified url, it shows the message below

Warning: Cannot modify header information – headers already sent by (output started at /home/content/p3pnexwpnas06_data01/03/2445603/html/wp-content/plugins/easy-sign-up/lib/esu-form-process-class.php:48) in /home/content/p3pnexwpnas06_data01/03/2445603/html/wp-includes/pluggable.php on line 1196

Note I’m not a web pro….still learning.
Any ideas will be appreciated. Thanks.

https://www.ads-software.com/plugins/easy-sign-up/