Are you receiving an error similar to this one when logged in to or attempting to log in to your WordPress Admin Dashboard?
Warning: Cannot modify header information - headers already sent by (output started at /domain.com/public_html/wp-content/themes/my-theme/functions.php:179) in /domain.com/public_html/wp-includes/pluggable.php on line 1427
The solution is simple. You have empty spaces or line breaks either before or after your <?php ?> tag in the functions.php file. Delete this and the issue should be resolved.