Why is the use of the flush() function potentially problematic in PHP scripts that involve header modification?

Using the flush() function in PHP scripts that involve header modification can be problematic because it sends the output buffer to the client, which can cause headers to be sent prematurely. This can result in errors such as "Cannot modify header information - headers already sent" because headers must be sent before any output. To solve this issue, you can use output buffering to capture the output and headers before sending them to the client.

ob_start(); // Start output buffering

// Your PHP code that modifies headers

ob_end_flush(); // Send the output buffer to the client