When flush and header are used in php, an error is reported.

In php, flush and header are both used to report errors. I have output before the header. how can I prevent the following code header from reporting errors? Find a solution ....
// This is the code I added
Echo 'SD ';
Ob_flush ();
Flush ();
// The following is the system code, which cannot be changed.
Ob_start ();
Header ('status: 100 ');
?>

Reply to discussion (solution)

Ob_start (); put it at the beginning

Ob_start (); put it at the beginning
This is the system code and cannot be changed.