Warning: Cannot modify header information - headers already sent by (output started at /home3/xxxx/public_html/wp-content/themes/fervans-a/fervens-a/functions.php:1) in /home3/xxxxxx/public_html/wp-includes/pluggable.php on line 770

yakuter in bir temasında sidebar da değişiklik olurken bu hata çıktı.

temayı değiştireyim dedim :
Warning: Cannot modify header information - headers already sent by (output started at /home3/xxx/public_html/wp-content/themes/fervans-a/fervens-a/functions.php:1) in /home3/xxxx/public_html/wp-includes/pluggable.php on line 770

ne yapabilirim?